Here my 50 cents:
1/4 tone down is the tone your finger produces when the string vibrates on your fingertip, just after you release the string from the fret. This note will also be there when sustain is not enabled, but very short ofcourse.
The vibrating string has a smal retrigger effect when you release the fingerpressure: this effect is dependent on the phase of the string during the finger lift off: this is what makes it a 50% chance of happening. One half of the time the release mutes the string extra, the other half the string gets extra energy, hence the trigger effect. In general though, the envelop of the string leaving the fret should be decreasing. I tried a midimachine with aftertouch to fix that, I dont know if it worked, too long ago. I’ll have a look tomorrow.
In chromatic mode the effect is less, because then there is still an extra chance that the position of your finger is not exactly 50% between the 2 frets, but a bit lower. So you get also about 50% releasenotes, unless you fret the finger against the higher fret.
For chromatic mode in studio work, you can simply tune your guitar about 20 cents higher ( or 80 cents lower). That will take care of your finger being above the 50 cents down border.
For pitchbend modes, the easiest way to get rid of the dive effect, is to delete all downgoing pitchbends. As long as use no whammy, this should work. Notes that start with a silent string bend will not bend down, that is the negative side effect. You have to start every note with the base note, bend it up, to have it slide down again.
The midimachine “Bend Attack” has a knob to kill bend downs.