Now that I think about it, if you transposed to F, it should be choosing Bb based upon my code. Are you using the transpose by key setting or transpose by steps? I just created a song with your exact chords, set the key of the song to C, transposed from C to F, and it worked as you would expect. Dm, F and Bb were used. I also tried it when transposing by steps, and that also worked. What key did you choose for the song?
If you are using a minor chord for the key of the song, there are still bugs present with transposing with minor chords that won't be fixed until the next update is released.
If you are using a minor chord for the key of the song, there are still bugs present with transposing with minor chords that won't be fixed until the next update is released.