GR-20 problem

[ylib]

When I set the unit to a specific bank (for example synth or percusion) it changes automatic (without I do something) to another bank (mostly a bank lower for ex. "brass" or "strings". Even when my cable 13 pins is not in the unit, it still changes his bank after a while. However when I choose the "user" bank, it stays on that bank
can somebody help me with this problem??