I never got emails explaining anything.  I did finally get my payout yesterday (after 11 days without payouts).  It did indeed have 7.71% missing due to the difficulty adjustment near the end of those 11 days.  BAN wasn't doing partial payments during those 11 days but instead was picking and choosing who was paid, so not everyone took the 7.71% hit on as many days worth.

IMO, handling difficulty changes in PPS the way BAN does is not the brightest idea.  If there is another difficulty drop, before the drop anyone could set their payout for 24 hours and earn extra for nearly a day at the expense of the pool.  Likewise, always hop off and never let a payout cross an increase!  The pool can probably handle it though-- there are far more increases available to skim from those who do not know any better!