The blog TomKarpik.com reports that you can experience "horrendous data loss" if you move data from one volume to another, and the destination volume disappears midway. Karpik says he first encountered it in Samba, but it also occurs no matter the type of destination -- local USB, Firewire, network, etc. -- and that the bug dates back all the way to Panther and affects Leopard.

News.com quips: "If you're moving data ... don't trip over the cord."

Daring Fireball suggests a workaround: "When you wish to move a folder between volumes, do a copy in the Finder (by dragging with no modifier keys held down) and then delete the original on the old volume manually."

The default behavior for Mac OS when you drag a file from one volume to another in Finder is to copy the file, but you can move it -- deleting the original automatically - by holding down the command key. The Unofficial Apple Weblog calls that a "trick" and a "lightly documented holdover from OS 9."

When I'm moving data between volumes, I don't even delete the original. I just archive the original to a folder somewhere, so it's there in case I need it. Because computers are two-faced little monsters: They're all nice and friendly most of the time, and then they'll turn around and betray you when they know it'll do the most damage.