It's actually kinda weird - I can see in the code that before adding actions quassel-client (Qt4 version) checks if the notication daemon supports actions, and I know that notify-osd doesn't report them as supported, but neverthless quassel sets them and instead of a proper notification I get a fallback popup.
As I've just found dozens upon dozens of those popups I'll try to dig into that tomorrow.
ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: quassel-client-qt4 0.8.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-18.29-generic 3.2.9
Uname: Linux 3.2.0-18-generic i686
NonfreeKernelModules: wl
ApportVersion: 1.94.1-0ubuntu2
Architecture: i386
Date: Wed Mar 21 23:45:47 2012
EcryptfsInUse: Yes
InstallationMedia: Ubuntu-Netbook 10.10 "Maverick Meerkat" - Release i386 (20101007)
SourcePackage: quassel
UpgradeStatus: Upgraded to precise on 2012-03-17 (4 days ago)
This is unlikely to be a priority for upstream, so patches welcome if you want a fix.