Yes ---if you mean OFP.
No---if you mean FMS. *
I don't think so, but I'm not sure, can't find any explaination in FCOM.
Guess the FMS is taking FF/FQ into acount for the next waypoint, thereafter its computations are considering a clean ship. Passing the next waypoint, same thing and so on... Therefore estimates of arrival fuel change every waypoint to a lower value.