First off, I'm using WinXP Pro SP2 with all updates to date installed and the latest versions of MsgPlus! and MSN (latest means I downloaded and installed the latest versions 3 days ago) and I use AlienGUISE for skinning (current skin is called Invader)

Whenever I switch between tabs in a tabbed conversation, the window they're in gets a bit smaller, until it can't get any smaller. The only way to counter this is to maximise the window.

I have 2 monitors, so it's not really a problem to have it maximised all the time, but it's really annoying nonetheless.

This is caused by your theming program (Windowblinds is known to cause this).