I've noticed this as well.
If you alt-tab out to windows, it doesn't seem like the battle gets paused, but instead everything seems to get slowed down.
If you flee the battle and then alt-tab, you have to wait for a bit before going back in order for this to work. If you go back in too soon, the flee-animation with you cowering is almost complete and you exit the battle resulting in the wild pet despawning.
Haven't checked how long you have to wait, but I guess it can be about 15-30 seconds or so.