I bought the Vox Tonelab EX second hand.

I read the manual.

There is one thing I don't understand, and I can't find anything in the manual about it. There are nog English tutorials on Youtube.

If anyone here could help me, I'd be grateful!

The question is about the "bank up" and "bank down" buttons to the left of the front panel.

Sometimes, they do what I expect: switch banks in the preset mode, and turn on / off pedal 1 ("bank down") or amps ("bank up") in stompbox mode.

Sometimes however.. they bring up numbers when pressed, running up to 25, then going back down. So they don't switch banks, and they don't turn on / off pedal 1 or amps. The manual does not seem to mention this behaviour.

When / why does this happen?

Again, I would be very grateful for your knowledge!