I don't think its the IBEC
We have one doing the exact same thing and there's no IBEC involved.
A friend asked me to maiden an ESM P-47 with a 20cc RCGF and when things were doing well I did a high speed fly-by down the runway and the gear cycled. Freaked me out, I immediately dropped the gear and circled and landed, figured something was loose or awry and I didn't want his new plane to total itself while I was holding the transmitter.
We have replaced the y-harness on the gear with a heavy duty one, run power direct from a battery to the rx without any switches, Horizon even replaced the retracts, it still does it. We can duplicate it on the ground by placing the plane in a cradle and starting the motor and advancing the throttle to about 40 percent and the gear will freak out.
So, don't waste your time chasing the IBEC