Mac OS X Panther-users have reported problems when enabling FileVault, a feature designed to protect user data, which seemingly doesn't, in some cases.

Claims exist that FileVault has reset or destroyed data for Safari, Address Book, Mail, Keychain, and the Dock. Manifestations include Keychain being reset, but also ceasing to store user passwords any more; Mail messages and Safari bookmarks have also been lost.

FileVault offers double password-protected 128-bit data security for user's Home directories, and is one of the key features in Mac OS X 10.3.

OS instability can also result from the problem, with user posts on Apple's support forums explaining that right now the only known fix is to format the drive and reinstall the OS.

Some reports claim that this data-loss has extended to other Macs, when users have synchronized plural machines using their .Mac account.

The problem seems to begin when activating a FileVault feature – available when users shutdown or restart their Macs on FileVault-enabled Macs – which offers to reclaim lost disk space in the Home directory it has encrypted.

It may not appear immediately that feature is used – some reports saying it has taken "five or six" restarts to appear.

Affected users have reported that the problem is rectified once they switch FileVault off, though data has to be restored and preferences reset.

Apple has said it is aware of and is investigating the problem.