Once you unlink the token from the NPC sheet, changes to the NPC sheet are not reflected in the token any longer. The reverse is also true, changes to the token bubbles are not reflected on the sheet. This is intended behavior so that you can have many instances of the same token and each handle things like HP independently from the other instances of the token. The way to make the math work is to click in the correct bubble over the token, a little box will appear and then just type the change in that box (not the whole formula). So, if your NPC was hit for 7 damage, you would click on the HP bubble and type -7 in the box and then hit return. It will subtract 7 from the prior total and display the correct result. If your NPC is healed for 5 HP, just click the bubble, type +5 in the box, and hit enter. System will add 5 to your health. Hope that helps.
