There are several cargo plane (C17, Galaxy and the dirty bog Antanov etc) that I know of plus a passenger aircraft ( BA something or other four engined city hopper) and a trainer(Gnat) all have anhedral that doesnt make sense to me as I wouldlt think they wouldnt intentionally make these aircraft unstable. A fighter yes I can see your arguement these types of plane I would doubt it.
The Anhedral takes the edge off of the over-stability - with such long wings roll control is already a problem, and extra dihedral effect is the last thing you want. It's not to make them "unstable" - just get them back to neutral.
Dennis