Windows 7's Bizarre Solid Color Wallpaper Bug

Microsoft engineers have explained why Windows 7 users experienced a 30-second delay when logging in to their computers, even after entering their passwords. The issue was caused by a solid color wallpaper being set as the desktop background.

The logon system waits for each component to report back that it is ready before moving past the Welcome screen. However, with a solid color wallpaper, the WallpaperReady signal never gets sent because the image-loading code doesn't run.

As a result, Windows 7 would idle for 30 seconds until its failsafe timer expires, causing the Welcome screen to stay on for the full time even if other components finished loading quickly. The bug was fixed in November 2009 with a Hotfix update, but users had already found a workaround by switching from a solid color to an image.

A related bug involving Group Policy caused the same delay when enabling certain policies that hid desktop icons and set the wallpaper to normal.