Maybe the structure of that disc? Which disc of season 2 will not split? Maybe someone else will have this set and can try it.
I think I see what is happening here. Since splitting a title is undesireable, DVDFab Split will put the titles on 2 discs without splitting a title when possible (such as 4, 40:00 episodes). There is nothing in the top window (Split Title) because no title needed to be split; this is like an automatic Customize Split, but with fewer controls and options. Customize Split is still better for TV episodes, try that instead. The screen capture is Prison Break, season 1 disc 2.