I want to use a part of my Excito B3 as Time Machine disk, however I don`t succeed in limiting the sparsebundle size. I'm running OS X 10.6.7 and it always tries to reset the size to the complete disk. If I make the Info.plist in the spareimage read-only, the Time Machine process crashes:

May 14 01:46:44 imac com.apple.backupd[579]: Resizing backup disk image from 95.5 MB to 1730.3 GB
May 14 01:46:44 imac com.apple.launchd[1] (com.apple.backupd[579]): Job appears to have crashed: Trace/BPT trap
May 14 01:46:44 imac com.apple.ReportCrash.Root[580]: 2011-05-14 01:46:44.870 ReportCrash[580:2803] Saved crash report for backupd[579] version ??? (???) to /Library/Logs/DiagnosticReports/backupd_2011-05-14-014644_localhost.crash

When the Info.plist is writeable is works fine, however it uses the complete B3 disk.
Am I doing something wrong or is this due to the latest update of OS X?