Thanx ChrisScott it more than helpful !
I fully agree with both you (Chris and Tom775) ... though the situation I was thinking for radar vectors was a really basic one: AP OFF + FD OFF + ATHR ON, without any FCU HDG or ALT selection -> (eg. the controller instructs you to fly heading 050 climbing to FL90, then you fly heading 050 manually with NO FCU selection, while starting a climb, to FL90 manually). In that situation, a FD left ON on a previous heading or ALT might also lead to unwanted thrust excursions, that's what I meant ... if wrong, could anyone explain the why ?!
I take it you have never flown the aircraft?
Tom775, haven't flown the bus yet, cause I'm yet a "pilot in the making" ...
Pensador, while flying with AP OFF, it would be best to turn the FD OFF whenever you're not going to follow it ... even if the example I made above is a bit uncommon to be sincere !