Wrong tab order on group creation by drag-and-drop
If I have two tabs next to eachother and I drag the right-side tab over the left-side one the resulting tab order in the newly created group is wrong: the right-side tab I dragged will be the first (leftmost) tab in the group and the former left-side tab will be the second (rightmost) tab in the group. The same happens if I drag the left one over the right one, but there it makes sense because the original order is kept. If I'm dragging the right one over the left one I expect the order to stay the same and it doesn't.
Good observation. Furthermore if you ungroup such a tab stack the original order isn't kept, they instead keep the order they were stacked in. Which makes sense, but yeah, it's a bug.
Here's another cute thing I just saw about tab ordering: if you move an entire tab stack past other tabs (1 position is enough) the tabs in the stack get re-ordered in some strange way. At first I thought they get ordered alphabetically by title but further testing showed they don't, the order just changes to something else.