Created attachment 4934 patch against 4.10.0 that fixes the bug When "change the background" is selected in the "Desktop" control panel, the background changes once, after the specified interval, and then stops changing. The cause of the problem is that the timer callback, xfce_backdrop_timer() in xfce-backdrop.c, does not return "TRUE" to indicate that it should continue to be called periodically. Instead, it returns void, and the calling function interprets whatever happens to be on the stack at the function return value address as a boolean. I've attached a patch against 4.10.0 that fixes this issue.
Thank you for your bug report. It has already been fixed in the git master branch and will soon be fixed in a stable release. *** This bug has been marked as a duplicate of bug 8962 ***