Change the TabItems layout when the TabControl OverflowMode="Wrap" with TabStripPlacement="Bottom" :
1. Let's say the wrap results in 3 lines. What we would expect is line 1 and 2 to be filling the entire width and line 3 to be partially filled. What we experience is line 1 partially filled and lines 2 and 3 filling the entire width 
2. When clicking on an item the lines swap around. The partially filled line can end up on top, in the middle or on the bottom. Clicking on items that cause tab rows to move up should re-flow the wrap.
3. Ideally - to look good - the logic should stretch the 'complete' rows to the entire width - i.e. it should adjust tab sizes to fill the entire width available on 'full' rows.