I am using bash and mintty. Ctrl-L does not clear the screen like it should:
0920:~$ ^L
-bash: $'\f': command not found
I get the same error if I've ssh-ed into a linux box via my cygwin mintty.
Sounds like an issue with your readline mappings in /etc/inputrc or ~/.inputrc. try adding this:
"\C-l": clear-screen