What it says in the pull request text. 

For example, if the plane had 5 degrees of aileron trim, the integrator would adjust so that eventually it was providing -5 degrees of aileron. Now suppose the airspeed doubled - the value of scaler would be halved, and the effect of the integrator would be halved, leading to a bank angle error until the integrator readjusted to the new airspeed. This isn't an issue when flying at fairly constant speeds or with only small trim offsets, but is a potential problem that should be fixed.

The solution is to move the speed scaler to the other side of the integrator, which keeps the same effective integrator gain, but means that the trim due to  integrator state will not change with airspeed.