I know sustain pedal is not usual on a harp, (unless you're Andreas Vollenweider)! But...
Depress sustain pedal, play and hold note, then release pedal - note holds as you would expect it to while still holding it.
Depress the pedal, play the same note twice, holding it the second time, then release pedal - note releases, even though you are still holding onto it.
Is this normal behaviour?