@dspk, really stupid question, but i have to ask: are you sure you’re not running a debug build of 0.7.1? (maybe a mislabeled one; if it’s debug, you should see some baudrate settings being printed on the screen at boot.)
otherwise, i agree with @ngwese that this sounds like a situation where the USB stack can’t keep up with the transfer requests.
i’m looking at some diffs and don’t think there was any change to the midi RX handling code itself. we added TX code but it shouldn’a have had an effect.
the most significant changes in 0.7.x were greg’s fixes to app pause/resume , especially nested calls. this greatly improved stability, but also means that interrupts are probably being disabled more often now. this gives the USB stack less opportunity to empty the MIDI RX buffer.
we could always try increasing the MIDI RX buffer size, but this is a sloppy band-aid at best.
i’ll look at it a bit more when i can and also checkout the fixes from earthsea.