Leopard uses would better skip use the the move option until Apple provides a fix for a recently discovered flaw. Apparently, the OS’s motto in such situations is “Delete files first, ask questions later”.

According to Tom Karpik, Leopard’s Finder is unable to check if the content moved from the hard drive to an external source has been copied there properly and will delete the files from the source regardless of the outcome of the action. Karpik wrote on his blog:

Leopard’s Finder has a glaring bug in its directory-moving code, leading to horrendous data loss if a destination volume disappears while a move operation is in action. 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.

I’ve now run tests on a Windows XP SP2 SMB mount, as well as a local HFS+ formatted USB drive, and the bug surfaces every time the destination disappears while the Finder is moving something to the destination.”

Apparently, the problem is available in Apple’s previous OSs, with Panther being the first one to feature it.

Apple is said to be getting ready to release the Mac OS X 10.5.1 and hopefully it will provide a fix for the flaw. Until then, just use the copy function and delete the files manually after making sure they have been copied successfully.