Hello again.
Humm, I am not sure about this one. I unfortunately only have a single, cheap USB midi keyboard here to test. Do you have an app that could display the "raw" midi status that your keyboard produces? If you could find that and send me the raw midi messages your keyboard outputs when you press + releast a note, that would help me a lot.
FamiStudio will determine key up/down by looking at the high-byte of status, similar to this table, which seems to be the stardard way of doing things.
On my side, using MIDIOX (a super old, terrible tool), it gives me status = 80 for a note off, and 90 for a note on.
* And no, there isnt any options for latency of any of that. That is not a high priority at the moment, and it would be very hard to make portable to Mac and the upcoming Linux version. Sorry about that.
-Mat