How to resume Windows 7 slideshow after restoring default wallpaper

I use SystemParametersInfo to remove the Desktop wallpaper.

SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, _T(""), SPIF_SENDCHANGE)   

later I restore it with the same method.

SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, NULL, SPIF_SENDCHANGE)
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That worked fine for all Windows versions including Vista. But with Windows 7 I found out that the desktop wallpaper slideshow will not be restored after setting the default wallpaper. Windows 7 displays the last shown image only.

How can I restore the desktop wallpaper and resume the slideshow ?