User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:44.0) Gecko/20100101 Firefox/44.0 Iceweasel/44.0.2 Build ID: 20160214092551 Steps to reproduce: Switch a movemail account to "maildirstore", re-install msgFilters.dat, restart Thunderbird then hit F5 to retrieve mails. Actual results: Emails {E} are retrieved into Inbox, and the first email E0 that matches a filter is copied (not moved) incompletely to the correct directory D, then no more filters are run. By "incompletely" I mean that the metadata of E0 is visible in D but I cannot view its contents. (I *can* view the contents of {E} in Inbox though.) Looking through the filesystem I see {E} in Inbox/tmp and empty files with the same name as E0 in D/cur. If I press F5 repeatedly, duplicates of {E} are retrieved into Inbox, the filter runs again and another duplicate of E0 as an empty file gets put in D with the remaining filters ignored. Expected results: Filters should run completely on {E}, with no remaining files in Inbox/tmp and no empty files in $D/cur. If I press F5 repeatedly, the subsequent presses should be no-ops (assuming that nothing else arrived in the meantime). A workaround that appears to work correctly, is to disable the filters (but don't delete them), press F5, then run then manually on "Inbox".