Lock roll and pitch values doesn't work in the extended tuning tab

The function lock roll and pitch values doesn't work in the extended tuning tab. I have this problem since updating to copter V3.4-rc1. So I'm no sure if its a Mission Planner or a arducopter firmware problem.

I use Mission Planner 1.3.38

Start by reproducing the locking failure in the extended tuning tab using Mission Planner 1.3.38 and the reported ArduCopter V3.4-rc1 setup. Trace whether the problem is in Mission Planner or the firmware; done means roll and pitch locking works reliably in the tab, with the responsible component established.

Written by the indexing model from the issue text.