Dear @Dmitri_Silaev,
Thanks making such detailed write-up 
, you are putting a lot of efforts in it.
To my personal opinion, but I could be wrong, you need first to un-group when you change the display column, and then to group again. Just to give the ability to give the software the ability to define on what to group! And because of this, it’s not a bug!
Dear @BenLee, would you mind to share Coda’s point of view 