I noticed that the Current Gear field is incorrect sometimes since one of the more recent firmware updates. I believe it gets messed up when the derailleur (SRAM Transmission, in my case) times out and goes into a power saving state. If I remember correctly, the Current Gear usually says "1" but maybe it's said "12" - I'll have to pay closer attention next time. Regardless, it is incorrect until I shift gears and then it is correct again.
I suppose it would be easy to say this is a SRAM bug, and it could be, but it seems to me that it started happening only after a recent Garmin firmware update. The only other time I've seen the Current Gear be incorrect was when my SRAM battery was very very low and it was cold outside.
I'll watch this more closely this week and update what I find here.