Stabbey; It seems what a Rush is being applied if the user is damaged in any way, not just under 30%
Fought skeletons, had 8 AP per turn at the start (fully healed I believe). Later on, I noticed I only had 6 left. Then when the archer shot me (from full health to 90% or so), it went right back up to 8. So yeah, not sure what's going on there, definitely not Working As Intended.