[...] In low light (indoors, typical nigh time illumination levels using artificial light) most of the time focus is OK, but on lower contrast targets it can fail, especially if you use a single manually selected AF zone. e.g the center AF zone. The odd thing is that under the same conditions, if you let the camera pick the AF zone from either the full set of 35, 25 or a target group, it will often get focus lock - and on exactly the same spot as the manually selected zone that fails. I would not cite this as a major issue (unless you habitually shoot low contrast targets in low light with a single manually selected AF zone), but it does point to something a little odd with the focus algorithm, or at least something that's not well explained in the manual. Perhaps in multiple zone mode the zones around the target (which, say, is under the zone in the center of the screen) assist the center zone in getting a focus lock? It does seem counterintuitive though that multizone AF seems to lock onto a low contrast low light target better than single zone AF does, even though the final AF zone (which is shown on the screen) is in exactly the same place.
It's possible that a firmware up date could address this issue, assuming Olympus acknowledge that something is a little odd. Perhaps it's supposed to work this way, but I don't quite understand why and it's not the sort of thing most manufacturers discuss in their literature, at least not on consumer level products. [...]