I have... yes, + docwood is right... check your calculation order.
Forms...Edit Fields... Set field calculation order... then move stuff up and down until it matches the order you want.

Also, Tab order seems to affect it and works best for me when the tab order matches the calculation order. (To change the tab order, first sort by tab order manually within the Fields panel "sort" drop-down. Then you can drag and drop fields where you want them within the Fields panel to modify the tab order.)

Then I have one PDF with 245 fields, that all are all calculated... that sticks now and then and won't calculate the grand total even with all the order correct. (it also crashes regularly when editing the form fields, i think i went too far!)

I added a calculate button with action mouse up do javascript "this.calculateNow();" Sometimes it gets "stuck" and I have to "tell" it to calculate with the button...

You can also add that action to key fields so it calculates on enter or exit etc.