KeePass Password Safe

Truecrypt's encryption is not weaker than KeePass'. What you read was a vulnerability that would allow attackers to know if a random file was infact a TrueCrypt volume. This vulnerability in no way helps the attacker gain access to the data inside, all it does is reduce the user's "plausible deniability".

Someone who has access to changed versions of your KDB *might* have a slight advantage if they apply cryptanalysis, but considering how hard KDB is to break in the first place, you needn't worry. However, if the master password to one of your former DB's is somehow leaked to them... then you should worry.

My advice: when you change your master password: Delete *ALL* backup copies that use the old password. And, if you change it because your old password was compromised, change as many passwords that the DB contained as you feasibly can.