Is there any disadvantage to importing a known private key, or easily crackable private key, into a wallet with other personal addresses that aren't meant to be public.
With Bitcoin-Qt the imported key with a prior transaction will show as used and won't then be used for change in the future. But not all wallets work that way, and could possibly send change to some other address from the wallet (e.g., chosen at random).
So, it is nearly ALWAYS a bad idea to import a private key into your wallet if you aren't sure that you are the only party with control of that private key.