Thanks for your bug report. When you click any of the list buttons, mIRC disables all of them, sends a requests to the server for the list and waits for a reply. If the buttons are not re-enabled, this means mIRC has not received a reply from the server.
On which IRC network do you see this issue?
If you enable debugging with /debug on (which outputs to a debug.log file), what does it show when you click on the quiet button?
