I have a similar and new problem with 20.0.1.2 on OSX.
Again, Brief, dealing with column select. In Python mode (and C mode), I created something like this:
def test():
#test1()
#test1()
#test1()
Now if I column select the hash (#) on all three lines, and hit delete to uncomment them, it deletes a space in front of the # (but not the hash itself), and places the cursor in the first column. Duplicating this in C code does the same thing.. Comments are not necessary, it happens with all code I tried it on. It only seems to happen when you have a single column selected.
I don't think happened on the previous version 20.0.0.X, because I do this type of edit constantly, and would have noticed.