Ok, this may not be a bug, just an undocumented (?) interaction. Here goes anyway:
* I was above max health thanks to overheal (health: 136 / 125)
* Drinking a Health Potion made me *lose* all my overheal health (so I lost 11 health), predictor indicated correctly what will happen ("Before" picture)
* Then Alchemist Scroll kicked in, and awarded me with +8 Max Health
* So my new health total was 125 / 133 ("After" picture):
"Thinker", just without the "ache".