Hidden Fields not Updated

Hidden Fields not Updated

I have two distinct but related problems with hidden fields, one older (carried over from the old UI), and one newer (new UI):

1.  The old one - I want to hide a formula field that I use to make a list (specifically, I extract the month from a birthday field, and make a list of birthdays by month).  But if I hide it, the birthday month never gets calculated.  Is there any way to get a hidden formula to update anyways?

2.  The new one - The Probability field isn't updated anymore if it's hidden.  This worked in the old UI, and I used it to trigger some Workflow Tasks.

Anyone else having these problems?