i tried it in my work on win7.
i have win 8.1 (although 64bit) at home, so i'll try it later on win8. maybe it's one of their quirks..
bbstyle? what's that? and how 
Here are some instructions:
In order to have separate wallpapers on each workspace you must add some settings either to the[color=rgb(119,119,119);]bbstyle.rc[/color] file or to a specific style file. This lets you have different wallpaper settings for different styles. If the settings are not found in the current style file, it will use those in the .rc file, if any. For example:
[color=rgb(187,187,187);]bbstyle.workspace1.rootCommand: [color=rgb(119,119,119);]bsetroot -solid black[/color]
bbstyle.workspace2.rootCommand: [color=rgb(119,119,119);]bsetroot -mod 3 3 -fg #666666 -bg #333333[/color]
bbstyle.workspace3.rootCommand: [color=rgb(119,119,119);]bsetroot -gradient verticalinterlaced -from rgb:00/00/00 -to rgb:99/99/99[/color]
bbstyle.workspace4.rootCommand: [color=rgb(119,119,119);]bsetbg -full backgroundsmypicture.png[/color][/color]
Note these settings have to be sequential, without any gaps, from workspace1 to workspaceX, otherwise BBStyle will only use the settings up to the first gap. If no rootCommand is set for a particular workspace, the default style rootCommand is used.