Mac Leopard users say they are losing files and folders when trying to move between volumes.

Users, developers and Mac bloggers have confirmed a serious bug in Apple's recently released Mac OS X 10.5 Leopard.

Moving folders or files between network volumes, or even between volumes on the same disk, can result in total data loss on both the target and originating locations if there is a disruption of the connection.

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First posted Nov. 5 by Tom Karpik on his blog, this bug has been replicated by other sites such as The Register and Macintouch.

"I first came across it when Samba crashed while I was moving a directory from my desktop over to a Samba mount on my FreeBSD server," wrote Karpik.

The data loss occurs only when files are moved, not copied, according to early reports. In addition, the data loss has been tied to moving files via the OS X Finder; manipulating files by using the "mv" command in OS X's Terminal application does not run this risk. Copying the files also seems to avoid the bug.

Normally, the process of moving files in the Finder involves creating new or modifying file references on the target volume, reading data to it, then deleting the original data. In Leopard, there seems to be an error that, when a move command is interrupted before completion—a network failure, or the target drive gets disconnected—the Finder believes the move is complete and processes the delete command.

Most users should not see this problem. First, it requires a connection interruption. Second, when you drag data between volumes in the Mac OS X Finder, the default behavior is to copy, not move (a change from the OS 9 days, inherited from OS X's Unix heritage); to move items between volumes, users have to hold the Command key down while dragging.

Still, this remains a serious issue. Apple is rumored to be well into work on a Mac OS X 10.5.1 update, though it is unclear whether a fix for this bug could make it into Leopard's first update.