Cannot move files to staging

Sometimes (quite often actually) files that I move to staging (Commit tab) simply vanish. They disappear from the left list (Unstaged) and don't appear in the Staged list.

I don't know when and why it happens. What I noticed though is that for such files no diff is shown in the Changes window above.

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: gitg 0.2.4-0ubuntu1
ProcVersionSignature: Ubuntu 3.5.0-19.30-generic 3.5.7
Uname: Linux 3.5.0-19-generic i686
ApportVersion: 2.6.1-0ubuntu6
Architecture: i386
Date: Fri Nov 23 16:21:31 2012
InstallationDate: Installed on 2011-10-06 (413 days ago)
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Beta i386 (20110921.2)
MarkForUpload: True
SourcePackage: gitg
UpgradeStatus: Upgraded to quantal on 2012-10-19 (34 days ago)