That's not a bug or glitch, that's exactly how it works and is supposed to work. Any Gmail or gaps account setup on with the phone (Menu/Settings/accounts - anything with a "G" next to it) is an option to use as an account in the market. The first gmail or gaps account you add when setting up the phone is going to always be the default account.
Theres no setup process to use an email account with the market. If the account is gmail or gaps and you agree to the TOS of the market, then it's available to download things from the Android market. A credit card is only added to purchase anything. If you never add a credit card to a gmail account, you can still open the market and still download free apps. If you tried to purchase an app is when you get a notification to add a card.
In this case you'd need to submit an enhancement, not a bug. You can submit enhancements to the
Android google code page after you search an verify the enhancement doesn't already exist. The enhancement you're looking for is probably something to the tune of " Under account settings for gmail accounts (Menu > Settings > Accounts - Gmail) please ad a check box to include or exclude the gmail account from list of accounts in the Android market."
Bug submissions take priority over enhancement submissions and you'd need to get people to go that specific submission and "star" it.