According to postings on various Apple sites, some users have reported two problems. In the most damaging fault, the Mac's hard disk is not available on start-up, requiring extensive recovery measures. The other fault seem to hit Mac PowerBooks, causing icons to slowly disappear from the desktop. An Apple (Nasdaq:AAPL) spokesperson was not immediately available for comment. Although unclear at this point, most of the problems appeared to be confined to users who have previously formatted or partitioned their hard drives with non-Apple products. But not all. Mac clone maker UMAX Data Systems reported problems while testing Mac OS 8.5. "While predominantly been problem-free, it has also resulted in the inexplicable loss of several hard drives," according to the UMAX posting. The problems occurred even with Apple hard drives, formatted with Apple's own Drive Setup software and installed in Apple PowerPC-based systems. "This problem is very elusive, but in some variations is fully re-creatable. It will probably affect only an extremely small number of users -- but to those users, its impact may be severe." Users said the first indication of a problem is the appearance of an icon that shows a disk with flashing question mark at start-up. "We regret that, to date, our testing has failed to conclusively isolate the cause of these losses," the UMAX posting said. "In short, there appears to be no way to predict a given drive's susceptibility to this problem, nor if a drive will be recoverable and can be re-formatted after the problem has manifested itself." Mac specialists recommend important data be backed up before installing 8.5. The problem has hit dozens of users, judging by messages posted on various sites. "Just thought I'd let you know that I also experienced the 8.5 hard drive kiss of death," wrote Richard Kelly on the MacInTouch site. "Although the most critical data was backed up it still represents a big loss of hours putting things back together."