When the arrows at the far right of the tab bar are inactive (hollow triangles), they can still be clicked on, and what results is unexpected.
For example, if you have only a few tabs open in a panel, such that all tabs are currently visible without scrolling, then both tab arrows at the far right are in an inactive state, as expected. However, no matter which one you then click on, the focus will change to the right-most tab.
Expected behaviour is that clicking on a "hollow"/inactive arrow will do nothing.
Windows 7 x64