Notifications are displayed as empty yellow baloon tips; the text inside the popup is not visible.
OS: Xubuntu 13.04 (Xfce)
Mumble is installed from the Ubuntu repository.
Style is set to System default.
Are you using that one?
Sorry, my verson is not that one from the repository.
I'm using mumble 1.2.4-1~ppa2~raring1.
I'm now using Mumble 1.2.4 under Fedora Xfce. Same problem here.
I'm using the Xfce theme "Xfce-darkness". Perhaps this is the root cause for the invisible text.