Had the same problem of wallpaper. The only way to get back to the default black, with weather animations, was to delete the contents -- not the key itself -- of the following two registry entries (at least, that's what it took for me):
\HKCU\Software\HTC\Manila\HomeBackgroundPath
\HKCU\Software\HTC\Manila\CachedBackgroundPath
source:
http://forum.xda-developers.com/show...postcount=1674