KDevCustomMakeManager failing to load in certain sessions?

Hi,

I just tried to create a new session from scratch and found it wouldn't load the KDevCustomMakeManager plugin when opening an existing project based on it. I got the same error in another session that had been using the CMake project manager only, but not in a session that already had a few projects open based on Manager=KDevCustomMakeManager.

In the end I got my new session by copying the sessionrc file from that last preexisting session and closing the unwanted projects, but I'd like to understand what happens here. There's no relevant output whatsoever on the terminal, not even when I set *.debug=true at the top of my qtlogging.ini file (despite what the comment above the call to QLoggingCategory::setFilterRules() in main.cpp suggests).

thanks,
René