Using setShadowCaster(True, some_res, some_res) with a resolution different than the initial shadow map resolution the light was created with, on a light that was created a while ago appears to lead to shadow bugs.
This seems to manifest in various unpredictable ways:
In my actual big project where I first noticed a potential issue, some objects simply stopped throwing a shadow even though I changed absolutely nothing else except just calling setShadowCaster(True, some_new_res, some_new_res) later a while after the light was created.
I then edited the basic shadow example (basic.py) as attached, to reproduce this issue.
In my minimal edit of the basic shadow example as attached, it seems to corrupt the shadow texture in some way (see screenshot attached) and it breaks 'v' which shows nothing as if either it was entirely bugged out or as if it had no buffers to show despite the light obviously using SOME sort of buffer still. If you comment out line 134, where I schedule the bug-introducing task, everything works fine again.
Ok someone on IRC just suggested this was fixed on the latest git master (I tried it with 1.9.3) and indeed I just built and tested 1.10 git master, and this problem appears to be gone! Neat!