I'm not sure what changed, but lately Vim has been driving me nuts. Whenever I try to do a column mode insert, vim takes my current character and adds to the last character I inserted. For example, the first time I do a block comment by inserting # on multiple lines, it works fine. The next time, however, I end up with ## inserted on every line, and the problem just compounds from there.

To do this, I'm hitting Ctrl-V, down or up arrow, Shift-I, #, and then Esc. This worked for months, but now it seems to be pasting extra stuff in. I've tried disabling all .vimrc files, but the behavior remains the same.

Any ideas?