[LAU] Sustain pedal issue with undesired repeated notes (m-audio keystation 88es + qjackctl + qsynth)

Hi, I have a problem I can't face alone on the digital piano I made on Debian Lenny with qsynth (v0.2.5-2.2), qjackctl (v0.3.2-1) and an m-audio keystation 88es keyboard. When I play the piano, some notes will repeat themselves after a few seconds only if I keep the sustain pedal pressed, just like a delay effect would do. I reported that only 4 notes are concerned for the moment, they have different repeat delays: G : ~7.5 sec (G4) G# : ~7 sec (G#4) A : ~6.5 sec (A4) A# : ~6 sec (A#4) Note that the notes above, relatively to the middle C of a piano keyboard called C3, goes from G4 to A#4. Could this be due to an hardware issue in the m-audio keyboard? Thanks a lot for any idea on how to track down and correct this (if possible). Nicolas.