Thanks for the hint.
I would have never tried this because for the third mouse button there is no "hold" function and it works as expected for moving forward/reverse. Now it also works with the second button as expected.
I would also say that this bug should be closed because it is not a bug, it is a feature. ;)

I got the same Problem with moving backwards. I hope this bug will be fixed because i miss it since ofp. :(