spectators get the command when using @p in a command block instead of the actual player trying to use it

Intended, if the spectator is nearer at the command block as the other player.

Indeed. But maybe it might be a cool feature if for example @u was implemented. This would target the player u sing the command block, clicking a sign or clicking in a clickEvent in tellraw. I know there is [c=1] but that still doesn't fix the problem. I think this might be very useful! 🙂