Yep, I think after trying new batteries or using a wall wart that's your next step. I hate it when things like that happen but there's always an explanation. Hopefully you'll be able to figure it out.
I've had my fair share of quirky little bugs lately too so don't feel too bad.
Just yesterday a board I made kept continuously resetting itself. Turns out that the button I used for the reset was to blame. I think I got those buttons from one of those electronic surplus/liquidation sites. The problem with those sites is that's where people dump their defective components.
Then this morning I borrowed a wall wart from one of my projects to power another board. When I was done and plugged it back in to the board I borrowed it from the board didn't work. Of course I'm like "WTF!" The problem there was that the plug is so wore out that it just wasn't making a good connection any longer. But it kind of had me worried for a minute.