If you have some lines selected and then do “Split into lines” you get multiple carets with selections. But when you run “Single selection” right after this, you'd get only first caret and selection and other selections would be lost.
My suggestion: if all of the selections can be merged to one, the resulting selection after running “Single selection” must include all of them. If there are gaps in selections, then all the first selections must be merged and the rest (after the first gap) can be dropped.
Customer support service by UserEcho