[soundboy35]

The only way I've been able to fix this when there are notes preceding a bit, is to go to notes view in grid mode,
select the area to duplicate or copy with the selector tool, and "trim to selection" (Command T), then duplicate, etc.
Sometimes it looks like the note is on the grid, but when zoomed in enough, you will see a tiny piece that precedes.
Why it won't quantize correctly in the first place is anybody's guess....