I have a similar issue, but not on bluetooth. And had same issue with my HTC Dinc1.
When playing audio via headphones with the non-stock music app (i.e. an audiobook player), the music app will randomly come on and start playing music (over/on top of my audiobook). Weird that this happens with both HTC phones I've owned.
Just started happening on the DNA this weekend after dozens of hours listening without incident, incidentally on mile 19 of a marathon, a point I really didn't want to be fuddling with the damn phone.