Talk:Game Updates/@comment-5312616-20131018042326/@comment-5786363-20131018125750

If your Magic meter reads 501+ / 1500 then you will not have the option to bu 1000 Magic until the Meter drops below 1000. Likewise the 1000 Magic disappars if you have spent 2000+ Magic already that day.

Basically it disappears based on how much Magic you have left to store and/or how much you have left to spend in the day.