I have a Logitech G700 and always used the Mouse Button 4 (Back) and 5 (Forward) (known as ThumbMouseButton and ThumbMouseButton2 in RO2's bindings section, respectively) for Throw Grenade and Reload.
After not playing for a while I came back and found that an update apparently cleared my settings (as usual), so I went to rebind my keys. The Reload would bind to the respective mouse button, but the Throw Grenade would not. I know the issue is not the actual button because I tried changing it in the LGS settings to a key on my keyboard and it worked, and I know it is not the option because other bindings would not work either with Mouse Button 5.
Is there something changed to disallow binding to the default "Back" button or what? I'd like this to be fixed rather than having to change my profile for RO2 each time I play.