Windows 8's uptake was stuck in reverse for the second straight quarter as the reputation-challenged operating system fell behind the pace set by Windows Vista six years ago, according to data released Friday. Web metrics firm Net Applications' figures for July put the combined user share of Windows 8 and 8.1 at 12.5 percent of the world's desktop and notebook systems, a small drop of six-hundredths of a percentage point from June. That decline was atop a one-tenth-point fall the month before, the first time the OS had lost user share since its October 2012 debut.