When we put in new ship date and due dates in a work order through WO-A and save the work order and say yes to recalculate estimated costs, the labor estimates drop off the estimated costs total.  This happens every time we change the dates.  The labor costs do not drop off if we recalculate without changing dates.
I wrote about this before but originally thought it might be due to not having labor costs in the routing for the part when the work order was first created.  This is not the case.  
We have the default Use estimated/projected $/hours set to E.

I am absolutely sure that the default is set as E.  But right after I said every time we change dates this happens, I tried a few more  and it's not every time, just what appears to be random.  I am looking at the start date to see if there is a date after which this doesn't happen.  Could it be that work orders released before we set the default (which was blank until we changed it) to E are affected but not ones after? ???

Sorry? How exactly is it that you are doing a work order for an "R" type item? Doesn't make sense.

I am having this problem every time I change the qty of a work order or use the copy workorder button.