WebEngine check fails against dummy threads

So, within a sys.excepthook callback I need to create an error menu with Qt and have that run on the mainthread. The slot mechanism appears to work just fine, as it ends up running on a DummyThread under MainThread:

<_DummyThread(Dummy-1, started daemon 17148)>

is the result of threading.current_thread()

I can also call Qt Methods just fine and make a Dialog.

However, the Dialog contains a WebView and then everything thinks it is breaking:

https://pastebin.com/KhGkprjJ

This looks like the Embedded Chromium doesn't know what a Dummy Thread is and falsely assumes it isn't the Main Thread. Or I could be completely off.

I've tried for two hours to make a minimal example also exhibit this issue and have failed to replicate it in a small example. No idea how to get you the information you probably need to fix this. The actual error seems to be send by the Chromium Process, as it seems to be coming in async, so trying to find a precise line where things go wrong isn't working out.