after loading an SF2 instrument a control message 77 (vibrato depth) causes the instrument to sound incorrectly.
suppressing the message helps only with Piano.
When preloaded with timidity sound is fine but then loading other instruments over the Java GUI has no effect.
Version 1.13 drops the 77 message (for piano only)
http://stackoverflow.com/questions/13315392/gervill-and-sf2-sound-incorrectly-on-some-midi-files