I'm glad we agree that it should at least not get into this situation where it
allocates memory endlessly and can thus disrupt other programs running on the
OS.

I compared the list of ProtoObject methods in 3.7 and 3.9 and see no
difference.  So it must be a change in the debugger code.  I also noticed it
happens on my 3.8-6326 unstable image.

Anyone have any ideas?