Okay, so here's a new twist for you (and maybe some diagnostics?). I cleared the cache on my computer last wekend,and since that time if I edit a pathfinder sheet's DEX (or create a new one), the DEX-related fields don't populate correctly, or at all (CMD, AC, Reflex). Now, if I edit DEX on my computer at work, I have no problems at all.
To add to the mix, it doesn't seem to matter which browser I use. Chrome, FF, IE all so the same thing.
Edit: I have the same problem when I create a new sheet. I do not get the same issues when I create or edit a 3.5 sheet.