It looks like Dorico makes the assumption that cross-staff notation somehow implies that the notes should be played by the other hand. Sometimes that’s the case, but very often it’s not. (That treble clef does not mean right hand and bass clef does not mean left hand is something piano teachers have to drill into students!)
What happens if you select the correct fingerings and use the propagate properties option? Does that force the score to be correct?
Also, you could fake an identical effect by merely using two voices in the lower stave and hiding rests above. Different steps to get there, but it would look identical, and you may not experience the bug this way.
Thank you! Now that I think of it, I did first move the notes to the lower staff and then I added fingerings, so Dorico understandably assumed the fingerings were meant for the left hand.