SlickEdit v12, WinXP.
If I have one buffer window open, not maximized, and use Window->Split Vertically, I have two windows but only one tab. I use Split Horizontally/Vertically quite often, and it can get confusing when there are fewer tabs than there are windows...
Similarly, if I drag a rectangle where there are no windows within SlickEdit, a new window is created, but no tab (if there is a window already open).