Effect Controls: Constrain playhead to useable frames
Currently, when working in the Effect Controls panel (with Pin to Clip active), pressing End takes the playhead to the end of the clip instead of to the last frame of the clip (one click to the left) and actually displays the first frame of the incoming clip. This necessitates pressing left-arrow to move one frame backward. Dragging a keyframe to the end of the window actually places it one frame beyond the last frame (which is actually useless). This behavior is quite annoying when Selection Follows Playhead is active, as the Effect Controls panel switches from the clip you're working on and displays the next one to the right.
Better behavior would be for the playhead to be constrained to active frames when Pin to Clip is active - unable to move past the last frame. Keyframe placement would also be constrained to active frames. Deactivating Pin to Clip would remove this constraint (though I'm not sure why you would need to scrub the playhead beyond clip boundaries if you're just moving keyframes around).
John Heiser commented
Attempted to edit the suggestion but can't. I was incorrect in remembering the behavior of the playhead when pressing End. It does go to the proper place. I guess the suggestion now is that keyframes be constrained from being placed outside active frames unless Pin to Clip is deactivated.
Pierre Louis Beranek commented
This is a great idea that's similar to my post here: https://adobe-video.uservoice.com/forums/911233-premiere-pro/suggestions/41067520-improve-snapping-in-effect-controls-window-so-it.
See the updated text and illustration I posted in a comment on that thread.