Windows 10: Dual Boot two Windows 10 Pro issues

Hello
I just build a new pc and I decided to go for a dual boot (one will be used for work: music production/video editing and the other for casual stuff, gaming etc)
each of the two Windows 10 is installed in it's own hard drive (two different SSD drives)
The first issue is that if I choose the second windows OS option from the boot menu the system will restart
I was informed about this from the tech guy that build the pc. He also said that he tried the legacy boot menu but the same problem exists
I suppose I can live with that, if there is no solution (if someone can think of something let me know)
But I also have another issue. I have bought two licence keys of course, but when I completed the registration for the 1st of my two windows, the second one became registered too! I tried changing the product key for the second one but as you might expect the key got changed for the 1st one as well
Please note that the two windows installations have different product IDs
Can this be resolved? Is it "right" to use two different installations with one key? I am not "whining" about buying a second license, I just don't want to run into any possible activation problems in the future

Here are my specs:
I7-7700K
Asus Maximus IX Code
Hyperx 32gb ram
MSI 1060 Gaming X 6G
Samsung SM961 (1st windows 10 boot option)
Samsung 850 evo pro (2nd windows 10 boot option)
other hard drives for storage (2xWD Black 1tb,1 toshiba 3TB)
PSU EVGA 850 G3
Cryorig H5 Universal CPU cooler

:)

 

Dual boot licensing, Win 10 x64 + Win 10 x64

I would like to install two instances of Win 10 Pro x64 on one computer and run dual boot. How many licenses are required?

 

Windows 10 Free Upgrade for BIOS-embedded Windows 8 Key + Dual Boot

I have seen the previous question
https://answers.microsoft.com/en-us/windows/forum/windows_10-windows_install/dual-boot-windows-10-with-same-copy-of-windows-10/5264e1de-0079-4dde-b7c3-dcfae5b8582c, but neither the question nor the answer is quite specific enough to what I'm asking or having
issue with.

I have two partitions that I dual boot between. Both are Windows 10 Pro free upgrades, based on a Windows 8.1 Pro key embedded in the Dell Precision T3610 machine's BIOS / SMBIOS. I've been using this configuration successfully since Windows 10 1511 or
1607 (guessing) without any issues.

This week I noticed that one of the two Windows 10 Pro installations no longer shows as activated. (We're on 1703 now of course; specifically 15063.540.) Truthfully I don't know when it happened. I only noticed because I went to configure taskbar properties,
and Windows show the "to personalize you must activate" message. I had also replaced my NVIDIA with an AMD video card a couple weeks ago; but again, I don't know if it happened then, nor have I ever had a video-card-only change trigger re-activation.

The activation error its giving on the second partition is 0xc004e016, even if I manually input the OEM Windows 8.1 Pro key retrieved from BIOS.

When I run the activation Troubleshooter, it reports "A digital license for Windows 10 Pro was found for this device running Windows 10 Pro. To use this license, you must install Windows 10 Pro." So it confirms that I have a valid Windows 10 Pro license
for this device (as expected), but then behaves as though Windows 10 Pro is not the version of Windows I'm already running (not as expected).

I guess the real question or maybe bug report I'm trying to get to here is:

Microsoft definitely provided me with "a license to run Windows 10 Pro on this device." But it appears as though maybe something is unintentionally (or maybe intentionally) not expecting "the Windows 10 Pro instance on this device is not just a static /
single instance." i.e. One way to look at this "dual boot between two different Windows 10 installations" is that it's "no different" than if I was doing a full disc backup & full disc restore to switch between the separately configured copies of Windows
I intend to run on this machine. I just happen to be dual-booting instead.

Is this scenario being accidently blocked, simply because the "a different but valid installation of Windows 10 could appear on this same device at any time" wasn't taken into account? Or is this a known an intentionally blocked scenario, in which case
a separate Windows 10 license is now needed (ever since 1703? 15063.540?) to keep the dual-boot configuration valid.

I guess I don't mind getting a second license too much, if that's really the specific requirement. But my next question will of course be "Will /that/ screw things up for a different reason?" i.e. One of my dual-boot Windows 10 Pro installations depending
on the BIOS-embedded Windows 8.1 Pro key with a free upgrade entitlement on this device, and the other dual-boot Windows 10 Pro installation being "a real license." Is that going to intentionally or unintentionally invalidate the Windows 10 Pro free upgrade
entitlement license that Microsoft's activation servers currently have "on file" for this device?

 

That is normal It will boot the default OS, if you change it it will restart. You could set the default OS to the one you use most in msconfig

I don't think you can do anything about that as the key is linked to the hardware. I have a disk that I boot on 2 different hardware (with 2 keys). When I swap between them I have to re-activate or wait for it to do it itself when it gets around to contacting MS servers.

Yours is the other way around - 2 Windows with 1 hardware. The key you enter links the hardware to the key on the MS servers. The EULA says you shouldn't run 2 instances on the same hardware:

I can't see how running 2 instances with separate keys can be achieved. If you were to install a 3rd version that would activate automatically as well as the hardware is already linked to your key.

Anyway you have bought 2 keys so you are complying (or trying to) even if it isn't possible to use them both.

 

What lx07 said +1. The restarting is normal when multi-booting a UEFI computer, and you tried to comply with the two license requirement, it's not your fault MS has changed their software making it impossible for you to attach a second product key to your second installation of Windows. The same situation exists with selling a computer with a retail license for Windows. You can remove Windows 10 from that computer and sell it and re-use your retail license on a new computer - but the old computer will still have it's digital license for Windows 10 stored on MS activation servers and the buyer can install their own Windows 10 on it and activate it for free with that digital license. But that isn't your problem, it is Microsoft's - you did all that you could to comply with the EULA.

 

Thank you guys for the help . My previous experiences with dual-boot was with 2000/XP and XP/7 where things were different.