I've never really been a fan of Rosegarden as a sequencer, I always found the timing far too loose and unstable (as it uses ALSA seq rather than Jack MIDI, the latter having rock solid timing), otherwise it is a very mature fully featured programme so this was a shame, with this in mind I began to write my own Jack MIDI sequencer some good progress has been made and I will still work on it at some point, however I've now found that using a small programmed called "a2jmidid" which bridges alsa midi through jackmidi, solves the timing glitches, I didn't expect it to at all and tried it on an off chance, but connecting rosegarden via this to jackmidi seems to solve the problem, great so now I can seriously use Rosegarden.