When the TreeView's ScrollViewer is Visible, changing the tree's width to 0 them back to Auto breaks the scrolling function of the ScrollViewer.
The workaround is to make the TreeView Collapsed before setting the Width to 0 and make it Visible before setting the Width back to Auto.

Reason for declination: 
The feedback item is declined due to duplication with the one below:
http://feedback.telerik.com/Project/143/Feedback/Details/113789-treeviews-scrolling-does-not-work-if-the-trees-width-is-set-to-0-and-then-back
Please follow it instead.