When receiving or after finishing a DCC file send I get a spinning beachball and the application stops responding completely so that a Force Quit has to be issued. It actually seems it's only the GUI which hangs, because if this happens during a transfer I can still see data being downloaded by using a network monitor. This problem also persists for me in the latests nightly builds.
Deleting the application and all related files, followed by a reinstall does not resolve the problem.