supposedly, modest keeps a process running if one has set automated mail check.

i have also found that modest may stay around in memory if hitting refresh without a currently active connection to the net (its not a sure thing tho).

https://bugs.maemo.org/show_bug.cgi?id=3610

but given its such a "minor" issue, and nokia seems to be going full speed towards fremantle, i fear its unlikely to get fixed.