On my side the note off is also a 90.
The keyboard i am using is an extremely vintage Yamaha portasound PSS-480 - Trying a different keyboard might be possible but a bit complicated at the moment.
Thanks for testing, very appreciated!
There is something changing in the DATA2 channel, which i think represents the velocity (?). It seems like zero velocity should be interpreted as a note off, something i definitely did not know.
UPDATE: I just read a bit on midi.org and found that indeed there are 2 ways to turn off a note. Zero velocity or a NOTE OFF code. Older equipment tend to use zero velocity, while newer stuff tend to use NOTE OFF.
MIDI Specification says : "A receiver must be capable of recognizing either method of turning off a note, and should treat them identically."
Ill prepare a fix and have you test it by email.
-Mat