This restriction is in place to prevent a situation where we (the house) could gain an advantage. We could intentionally generate future server seeds for your account that bias results against a previously chosen seed. We could, for example, generate a seed where the first few bets placed with your old or favorite client seed and betting style tend to have a higher chance of resulting in a losing bet. Disallowing reuse of a seed prevents this exploit from being possible.

The message is out of date indicating the restriction will be removed is out of date and will be updated shortly.