Ch1 and ch3's pwm output will exceed 2000

I use Ardurover 3.2 beta and with skid_steer_out=1.
I push the throttle to max, when i push the steer button to right(max), ch1 is 2250 and ch3 is 1750. when i push the steer button to left(max), ch1 is 1750and ch3 is 2250.
I want to modify the code but do not find the bug.

Hello,
We are working on a correction for this, it should be merged into master this week I hope ! See https://github.com/ArduPilot/ardupilot/pull/5819

@khancyr
i will test the code(https://github.com/ArduPilot/ardupilot/pull/5819)
thanks!