For those using Disabled 1 directives in your pound config, I just committed a fix. Tot_pri wasn't being counted properly at config load time, so you could end up with 503 errors.
Test case: Create a disabled backend with a priority of 5, and an enabled backend with a priority of 1. You have about a 16% chance of a request working, otherwise, it'll throw a e503 no back-end error. Fixed in both pcidss/v2.6 and stage_for_upstream/v2.7b Joe