I've had this happen twice now. I'm hunting for a rare Scalded Basilisk Hatchling and switch-training a lowbie pet at the same time. My team consists of a level 14 in the first slot, a level 23 in the second, and a level 18 in the third. When I'm battling the basilisk, it'll feign death and swap with one of its own team members like it's supposed to - except when it's the last pet standing. It'll feign, my attack will miss, and then it'll force my team to switch the active level 23 with the level 14.
The Feign Death tooltip says nothing about forcing the opposing team to swap, and even so, it does say that the user swaps with the highest health pet - which my level 14 is clearly not. Has this happened to anybody else?