I fixed it by compiling a cvs-snapshot of hald. Now the property
"volume.is_mounted =" behaves correctly.
http://www.freedesktop.org/wiki/Software_2fHalBuildInstructions
I used /usr as prefix and installed. The init-script and the policies
are used from hal-0.5.4 package, i didn't need to modify anything.
Seems like the current release hal-0.5.4 is buggy.
--
When it came to making bad movies, Ed Wood was the best.