Apple is distributing test versions of a bug-fix upgrade of its new Leopard Mac OS. 10.5.1 fixes bugs in the firewall, data lost problems, and bugs in Mail, Spotlight, iCal, and more, according to Engadget, which lists a couple of dozen bugs that the update fixes.

The update, Mac OS X 10.5.1 build 9B13, weighs in at 267 MB, according to AppleInsider, adding that one of the bugs being fixed in the release involves moving files across partitions -- possibly the same as the widely publicized data loss bug that can hit when moving files and folders between volumes.

Likewise, the update also includes a firewall fix. Leopard's firewall received harsh criticism from Heise Security, which noted several appalling flaws, among them: The firewall is switched off by default when Leopard ships on new machines. Moreover, users who previously switched the firewall on in earlier versions of Mac OS X -- Tiger and earlier -- will find the Leopard upgrade switches off the firewall. No word on whether the firewall upgrade in 10.5.1 addresses the flaws Heise describes.

AppleInsider expects Apple to release the final version of the update in a few weeks.