Astral Tree stamina bonuses are not included in HP calculation on Levelup

With my normal gear and stats, my character has around 1800 HP. With the Astral Skill Tree Stamina branch active, this increases to around 2800 HP.
When I level up while the Astral Stamina branch is active, my current HP is set back to around 1800, as if the Astral Stamina nodes were not active.
If I understood correctly after discussing this with Phrezz, the level-up HP calculation seems to use only the character’s normal stats and does not include the additional Stamina/HP from the Astral Skill Tree.