Created folder called "D:"

We had a guy use RapidSVN (on Windows), and SOMEHOW, he was able get the
files into the repository like the picture below. I tried deleting them
in Tortoise and the command line, and both bombed. I ended up using
svndumpfilter to remove it. Anyone ever see this happen? I was unable
to even recreate that structure in a different repository.
 
We are back up and running, but I didn't know if this was a bug that we
should report, or just not mention again.
 
Thanks!
Jason