Nothing serious, and it makes a lot of sense. I just didn't think about it.
I withdrew my money from the site last week, because I didn't want to risk losing what I had in there in case I hit a bad run. I decided to put it back in because of the 25% deposit bonus. So, I put $100 in with my bank card, but didn't get a box for a bonus code. I e-mailed support about it, to see if I could get the 25% bonus (it's valid until the end of tomorrow IIRC) - Here was the response I got:
"Hello Brett,
Thank you for contacting PokerStars.
The reason that you did not have the option to input the bonus code was
that you made a withdrawal on the 16th. Withdrawal's before making your
deposit during the promotion period voids the offer. This eliminates
players withdrawing and then re-depositing funds already in their account.
If you have any further questions about this or any other matter, please
don't hesitate to ask.
Good luck to you, and thank you for choosing PokerStars.
Regards,
Randy"
So, it makes sense, but if you're planning on depositing during any bonuses in the future, make sure not to withdraw in a somewhat recent timeframe

- oops!