Hello runes,
The property is used when you have multi-row tab items (The tabs move to another row when the IsBreak property of a TabItem is true). The ReorderTabRows property specifies whether the rows will be reordered so that the selected tab item will always be closest to the content.
This xaml demostrates this:
<telerikNavigation:RadTabControl
ReorderTabRows="
True">
<telerikNavigation:RadTabItem Header="Item 1" />
<telerikNavigation:RadTabItem Header="Item 2"
IsBreak="
True" />
<telerikNavigation:RadTabItem Header="Item 3" />
<telerikNavigation:RadTabItem Header="Item 4" />
</telerikNavigation:RadTabControl>
Sincerely yours,
Miroslav
the Telerik team