When I hold the sustain pedal and tap a key, the piano roll will show this key as if it were being held.

A quick search confirms this is the default behavior of FL Studio (very weird).

This Youtube video is one of the first hits I got:

     https://www.youtube.com/watch?v=JF2kt0o2kVY

I didn't watch the whole thing but I presume it tells you how to change the behavior.

I've just now obtained a Roland LX705, and am trying to record its MIDI output to use it with Pianoteq 7 on FL Studio.

I've configured the keyboard as a MIDI input device, however the sustain pedal of my piano isn't doing exactly what I would like. When I hold the sustain pedal and tap a key, the piano roll will show this key as if it were being held. If I release the sustain pedal, the key is released, and I cannot "keep" the sonority of the key even if I quickly hold the sustain pedal again.

Contrast that with using the sustain pedal on Pianoteq's interface, and when I tap a key, it will only show up as a very short press on the piano roll, but will keep sounding. If I release and hold the sustain pedal quickly, I am still able to hear the key being played.

I see that you can configure Pianoteq's pedals to listen to a MIDI controller, however if I try to set the MIDI controller of Pianoteq's pedal and then press my piano's sustain pedal, nothing happens. Is there a specific setting I could set anywhere to enable this? Would I need a separate sustain pedal that can be recognized as a MIDI controller?