Yep it seems like a bug. Sometimes someone can text me 5 minutes after I text them, and they will still appear above my text, like they did it before me, but the timestamp is correct, just not the order.
I have powercycled but still does this. I thought I figured it out, that if I clicked X in the corner of the popup it would put it in the right order (worked a couple of times), then go read in the chat screen. But since it has not worked. I agree though, a little irritating when they are out of order but not a massive problem.