Version:            (using Devel)
Installed from:    Compiled sources

$ find wallpapers/ | wc -l
3152

When using the slideshow wallpaper plugin, a dialog scanning every wallpaper on the wallpers directory shows in modal mode and blocks interaction on:
* Desktop start
* Desktop restart
* Desktop preferences

for several seconds.

If it really should scan (what for, I guess), it should be on background without modal dialogs. It should not delay wallpaper drawing either. Also, caching this data should be done too, as this dialog pops up every time preferences are shown.