I've noticed this also, I ended up switching it to use the Systray balloon messages instead for the time being.
From: Chris Maciejewski [mailto:email@example.com]
Sent: Tuesday, 12 July 2011 6:57 PM
Subject: [jitsi-dev] Systray pop-up too small
It seems to me there is a bug in SystemTray pop-up window.
It is currently too small to accommodate some of the messages.
Please see example below:
Tested on nightly.build.3576 - Windows 7 32bit.