Disfunctional thunderbird due to compression of folders

When I search through a local folder (seperate from the IMAP Inbox), first off these are compressed into *.msf files. If these are present, upon the next start of thunderbird it is no longer functional, the GUI pops up, the folder tab visible, also the header tab but no mail is visible and thunderbird locks up. The only way to get it working again ist to kill thunderbird, delete the *.msf files and then restart thunderbird.
It is version 2.0.0.6 running under OSX Tiger 10.4.10