I'm user of Wallch. Wallpaper changing makes my 2x 2 GHx proc choking if the video is being played at the time. Or put programming work instead of watching video, that results delayed actions.
I've reported the bug to Wallch devs https://bugs.launchpad.net/bugs/1340980 and it seems depended on GNOME, not Wallch.
I'd be glad for a way to simply disable fade effect for wallpaper change.
Edit: for now I've given up and just modified wallpaper change
delay to 2 hours... No answers :( .