Either I'm experiencing software amnesia or else some setting changed in Zbrush, but now I am unable to pan or zoom using the hotkeys, only rotate. Additionally, the Preferences > Hotkeys > Restore button is grayed out. Did I mess something up?
Edit: Interestingly, the Ctrl + D divide geometry hotkey combo has stopped working as well.
EDIT 2: Don't know what was wrong, but now it works again.