I'm investigating, if this is data related. If it does, a factory reset obvioulsy helps.
Not sure, what "filtering" authors in Browser Mode really means. You can sort by author or select the View "Current Author". For both, if you do, the Up and Down buttons often make little sense. If I select a Rig of Lasse Lammert - Rig Name starting with "LL - " - and change the View to "Current Author" and then use the Up/Down button, which normally takes me to the next/previous starting letter, in this case it can just switch between the first and the last Rig staring with "LL -" as all Lasse Lammert Rigs are starting with "LL -".
Or what do you expect from this function: filtering by author and loading a Rig with the following or previous starting letter?