Well okay here's an example from my situation. I am using a long press of my "shift lock" key to put my Empeg into standby. Here's the relevant definitions:

[ir_translate]
; The shift key
AD520C.L=20df03.L ; press and hold "ATT" = standby
AD520C=FFFFFFFF.S ; "ATT" = Shift Key

When I hold down the button, my Empeg doesn't go to standby until I release it. I agree that for FF/REW, it makes sense to hold onto the release code. So maybe it should be configurable with a modifier as you have stated. Unless I'm doing something wrong with the above definitions... There are other buttons I have which have the same behavior, such as the AM/FM buttons:

AD520D.LT=20df07 ; AM/FM in tuner

This one doesn't execute until I let go of my "source" button. Are you seeing the same thing with any of your remotes?