A signed mail shows up in the folder/item list, but when touching it in order to read it, the mail is displayed without body. In this test, the sender and its certificate were not known. No indication of that fact can be seen. Observed in version 4:4.5~20100910.1175630-1maemo6.1174786 .
Mmh, after a restart it worked. Might have to do with sync problems. Leaving issue for further investigation, but downgrading prio and severity.
Did this happen again?
Retested with 4:4.6~20101130.1202227-1maemo1.1202030 and didn't happen again.