-checkaction=C - Debugger out of sync?

[frame]

In Visual Studio I can step into a thread and hold on a while. By 
resuming the next instruction some invariant kicks in and throws 
an error but it doesn't hold the thread in the debugger - I just 
see the error on the output.

The debugger is still active but now running from 
`rt.lifetime.finalize_struct(...)` (at least this is shown in the 
stack window) while executing the next step of my user code in a 
already half destroyed struct.

Setting a breakpoint on the invariant assert does not work. In 
detail it's some Schrödingers assert:

If I set a breakpoint without holding the thread on, nothing 
happens and all variants are fine. If I hold the thread on with 
the breakpoint set and then resume with the next step, also no 
error appears. But if I do the same with disabled breakpoint, the 
error is thrown in the output.

It's the same thread, I checked it with GetCurrentThreadId(). 
Also the invariant is in the same thread checked, so the debugger 
is somehow out of sync while the program flow is ahead.

Then I checked that I have supplied `-checkaction=C` on the main 
app while a DLL was compiled with default settings. After 
changing the DLL, the error disappeared. Is this just a 
coincidence or can `-checkaction` cause a stack corruption or 
something?