I set the width of my vertical tabs by dragging the right border of the vertical tab bar.  I right-clicked one of the tabs and clicked New Vertical Tab group.  The width setting of the original vertical tab bar was lost and now the tabs in that bar now had different widths.  In the New Vertical Tab Group, I right-clicked the tab I moved over to that new tab group, and clicked Move to Previous Tab Group.  The tab moved back to the original vertical tabs group, but the original width of the vertical tabs bar was not restored.  I moved the cursor to the left of the new right border of that vertical tabs bar, and the gray vertical line for setting the vertical tab bar width appeared.  I dragged this gray bar to the desired width and the the vertical tab bar width was set.  The tabs were no longer of different widths, but now all had the same width.