I'm using bitcoin-qt. Suppose that one of the private keys in my wallet is compromised somehow, and is released to an attacker or the public. Of course, I can transfer all the coins from the compromised address to a new one (unless the attacker does it first). However, bitcoin-qt apparently doesn't provide a way to delete or disable a private key from a wallet. (This is understandable; it would be pretty bad to accidentally delete a private key for an address that had coins in it.)
Is it safe to leave the key in the wallet, assuming I never again intentionally transfer any coins to that address? (I could label it DONOTUSE or something.) Or are there situations (e.g. change) where the client might automatically transfer coins there without asking me?