Gmail plasmoid double notifications

Every time I get an email, I receive a couple of notifications for that email and the notification sound plays twice as well. If I disable the notifications for gmail plasmoid, I don’t get any notifications at all - which means that the double notifications are really triggered by gmail plasmoid. Any ideas how to change that?

I’m running OpenSUSE 11.3 and I’m fairly new to Linux.

I use the Firefox addon 'Gmail Manager.
Never tried the Plasmoid. It seems to have a couple of repos, both classed unstable - could be something to take to the Mailing List for discussion
or IRC #opensuse-kde