Compressed scores and triplets

I just ran across a SATB compressed score that has occasional triplets. I like to give each voice its own staff, so I mark the lower notes as voice 2, copy them to the alto or bass staff, flip the voices, and delete the rests. It isn’t possible to mark the lower notes of triplets as voice 2. The work around is easy, I just copy and paste the triplet run, and delete the notes of the other voice. Is it possible to look into why the lower notes of triplets cannot be marked as voice 2?