I'm using Rosegarden (the version that comes with Ubuntu 14.04) connected via MIDI to a Yamaha Clavinova CLP-430. When recording and playing back, the ends of notes are being prolonged, seemingly decaying slowly (something like ~600 ms). But the duration varies; occasionally a note decays quickly.
One strange thing is, in a particular music session, it may either happen or not occur at all. So far in 6 sessions, the issue has been present 4 times, and the other 2 times it didn't occur at all.
I haven't investigated the data going over the MIDI bus, but my guess is that Rosegarden may be fiddling with note-off velocity.
If I take out Rosegarden, and just use QJackCtl to connect MIDI in directly to out, then it doesn't happen.
I've tried it with both the piano's in-built USB MIDI interface, and also with a separate MidiSport USB-MIDI converter. The problem occurs with either one.
The problem seems to only affect live MIDI playback. If I record, then export the recording as a MIDI file, and then load the MIDI file onto a USB memory stick and plug that into the piano, then play that MIDI file on the piano, there is no problem with note-off velocity.