I have also noticed a problem with the EM5 focusing with my 12-50 lens when shooting macro. I was night diving in Raja Ampat. My shutter speed was set to 1/250, with 200 ISO, (on full manual setting) but I had quite a lot of difficulty with subjects that had very low contrast. Even using my Sola 800 at full power didn't help.
I ended up focusing on something else close by, locking the focus, and then "rocking" to adjust the focus. Is that just the nature of the EM5?
I was a previous D200 shooter (Subal housing).