This happened last weekend already.
While levi hunting patrizio and I seem to have taken the central skirmish mission at exactly the same time, resulting in two active missions for the whole group.
IIRC after killing the levi the mission board went back to normal but one of the missions stayed active in the mission log until I logged off.

screenshots:
http://kitchen.nfshost.com/ven/twomissions/

Are you sure that this bug was caused by you and patrizio taking the mission at exactly the same time? I wouldn't expect the two instances of the mission to be listed in separate categories (combat and general) if that were the case...

Dunno .. I haven't seen this kind of thing before. And we docked at the same time.