This is not a bug, because the modifier you put on the spell sheet page is not linked to the attack section, and never was. Doing that would be problematic as you would then not be able to set either of them individually, they would always have to be identical and that is hard to do when multiclassing. If you want to have modifiers like that, you are going to have to set them for each thing individually.
I was assuming that the attack entry was searching the spell page to see what section it was in and using the appropriate entry (but I did not test it). I guess it could be a problem for something like cleric/paladin or warlock/wizard if the same spell appears in multiple sections.
Adding the modifier for spell attacks was easy enough (just add the +1 to both spell page and attack entry). However, I don't see a way to modify the spell save DC for attack entries that have a DC (the modifier seems to need to be "dc" to pick up the DC and "dc+1" did not work). Is there a way that I'm missing to modify the spell save DC on the attack entry?