Basic Info:
In command block: "/spawnpoint @p" used to be able to set spawn of the character to their current position.
NOW it says invalid and requires format: "/spawnpoint @p x y z" or some other input

I have been working on an adventure for well over a year now and implemented MANY command blocks that would be activated by pressing a button and would then set your spawnpoint to your exact location. It was working fine until more recent snapshots so assuming this is a bug as I know many adventure maps would break from this function being taken out.