I think it has to do with voice allocation, or whatever it's called. On an 8-voice Rev2, if the first key pressed is a C1 for instance, which gets allocated to voice 1, then you press a C2 which gets allocated to voice 2... the next to voice 3 etc etc... when you've played 8 notes already, the next (9th) note again gets allocated to voice 1, starting the cycle over again. Let's say you play a G3 as the 9th note, it will then start gliding from C1, which is where voice 1 is still at until it gets assigned a new pitch. The next key pressed, the 10th in succession, will glide from whatever voice 2 is at, in this case C2, to whatever key/pitch you play as the 10th... and so on.
The voices "rotate", as to minimize potential voice stealing probably (ie not killing a decaying note... like if you have set long release times), which is a good thing, but when it comes to glide... well, it gets hard to predict where the start point of the glide will be, unless you have a strictly sequential (no pun intended) pattern that is predictable. In this case, using an 8 step sequence with an 8 voice Rev2 would give predictable results.