So the process of finding these is not that easy but not that hard either, I'll put it here so future visitors don't have to research / experiment.
- Download @Anders Melander's Map2pdb, compile it and run it against your applications .map file. You'll get a .pdb file.
- Download WinDbg and install it. Once done, go to File -> Settings -> Debugging settings and add the folder where your .pdb file is to the Symbol path list
- Launch your application and when it's in the state you want to examine, go to File -> Attach to process and select your application.
- In the lower-right pane select the "Threads" tab and double-click the offending one (TID = ThreadID in HEX)
- Now go to the Stack tab and if everything is good, you get readable stack traces
In my case @Stefan Glienke was absolutely right:
As I am not using thread pools, I need to find out what does... and get rid of it, somehow...