This has been a problem in PB for a long time. There is absolutely no reason why the onus should be on the user to remember to return focus to the plex by pressing F3 or clicking the plex each time before clicking Back or Forward. It might be different if Back/Forward had a different action in Notes, but they don't - the two functions are totally independent. This means three extra chores for the user - focus on plex, go back/forward, re-focus on Notes.
PB should not disable the Back/Forward buttons when Notes has focus. Instead, it should recognize when they are clicked (or the accelerator keys pressed) and automatically move focus to the plex, change the active thought back/forwards, move focus to the note of the new thought and to the last cursor position in that Note. This would enable users to copy/paste between notes without having to worry about transferring focus back and forth all the time.
Moe, I'd appreciate it if you would forward this request to the engineers.