If you input a note and tie as in Ex1 and then select the note and press R for repeat you get Ex2. If you select both notes in Ex3 and press R you get Ex3 you get Ex4. Clearly this is inconsistent and therefore one of these is a bug.
These situations should not be confused with when the whole bar is selected when both situations result in the tie being copied. This is then consistent and I think correct (the tie is part of the bar)
It is my opinion that it is the situation with two parts i.e. Ex3 and Ex4 that is the bug. When a note is selected only the note should be repeated. This principle is also consistent with how Sibelius treats notes with harmonics, cuivre and accent signs. Only the note is repeated not the attached sign.