Interesting. I'm not exactly sure why they would remove the funds like that.

Did you by any chance hit a "random jackpot" during your play? I know they remove those from your account if you won them using a free chip.

Otherwise, I would shoot them an email to see what they say. Obviously they wouldn't allow you to cashout the full amount since it was on a free chip, but it's a little strange that they would take the money from your account in the middle of your play.