tumbler prevents unmount of archive

After mounting a zip archive in Marlin and try to unmount it again, I get an error message saying that the device is in use by a process "tumblerd". No file of the zip archive is opened in any graphical program, and the archive is also not opened in a tab of the file browser.

I tried killing the process (sudo pkill tumblerd), but now the error message says that the device is in use by an "unknown application (26728)". I don't know what 26728 is, but it seems not to be a process id.

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: tumbler 0.1.25-1ubuntu1
ProcVersionSignature: Ubuntu 3.5.0-18.29-generic 3.5.7
Uname: Linux 3.5.0-18-generic i686
ApportVersion: 2.6.1-0ubuntu6
Architecture: i386
Date: Tue Nov 27 18:42:44 2012
MarkForUpload: True
SourcePackage: tumbler
UpgradeStatus: No upgrade log present (probably fresh install)