Terrytigre,
Thank you for being observant and raising this issue. In this case, it is working as intended. Here are the details:
If you get a temporary buff to your constitution, your maximum HP will be increased, however your current HP will not change. You can heal or regenerate up to the new maximum. If the temporary boost in constitution is removed, your maximum HP is reduced, but your current HP remains unchanged, even if it is higher than your maximum. While your HP is higher than your maximum, you cannot regenerate further or be healed further, but you don’t automatically lose the HP. This gives you the option to buff again without having to heal up again. I think you will appreciate when a buff wears off in the middle of a fight but doesn’t leave you suddenly at low HP.
Warning: If you change equipment while your HP is above the maximum, your HP will be set back to the maximum, which prevents exploits like wearing something with high CON and healing to max, then switching it out again.
Thanks for playing!
Amon