Why does Unity keep changing the CPU setting on my DLLs?

I'm using Unity 2018.3.0f2. I have some custom built DLLs that I've built for different architectures. Among them are a version for x86 and a version for x64.

Unity naturally complains that there is a DLL collision:

Multiple plugins with the same name 'uwpbridgedll' (found at 'Assets/UWPBridgeDll/x64/UWPBridgeDll.dll' and 'Assets/Plugins/UWPBridgeDll/x86/UWPBridgeDll.dll'). That means one or more plugins are set to be compatible with Editor. Only one plugin at the time can be used by Editor.
UnityEngine.GUIUtilityrocessEvent(Int32, IntPtr)​

So I went to go set each DLL to be specific to a particular architecture. Crazy thing is, every time I change the architecture on one, Unity changes the architecture on the other to match, so they stay colliding! Watch:



What's going on?! Why is it changing the setting out from under me?

 

Platform settings probably sharing same UI elements.
But I suspect, once you apply settings on right, left settings of dll are not overwritten, other than UI elements.

I suspect problem is more, that you have two files with same name uwpbridgedll, irrespectively to the directory, where they are.
Hence conflict.

 

@Tautvydas-Zilys Just filed it. Sample project included. Bug ID 1126671.