Enchantment, 2U (3) Each player can't play more than one spell each turn. "Too many wizards spoil the spell, but too many spells spoil the wizard. -Sign on entry to arcane lab "
Illus. Brain Snoddy
You cannot play a buyback spell more than once. It does not matter that it's the same spell card. It's not the same spell instance. [WotC Rules Team 1998/10/18]
If the spell is countered, it still counts as the one spell played. [D'Angelo 1998/10/19]
When it enters play, it will look back over the turn to see if any spell was cast before it entered play. [DeLaney 1998/10/17] It will notice itself being played. [D'Angelo 1998/10/22]
When it leaves play, the effect ends and all players are able to play spells unrestricted again. [D'Angelo 1999/11/23]