You only had to close Blender through File -> Quit.
Leaks happened because WM_exit() was called from within operator, UI wasn't able
to free some of it's heap data then. This data was the handler added in
uiTemplateRunningJobs() and the IDProperty group added in uiItemFullO_ptr_ex().
There was obviously a general design issue which only became visible in this
specific case.
We now delay the WM_exit call by wrapping it into a handler that gets registered
as usual. I didn't see a better way to do this, all tricks done in
ui_apply_but_funcs_after() to prevent leaks didn't work here. In fact they may
be redundant now, but am not brave enough to try ;)
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