Actually, looking closer with this, the DisplayName column has been on that table for a long time. All we did in 22.214.171.124 is allow setting the display name on creation of a role and changing display name on updating a role. The way it used to work was it just used the same value for DisplayName and RoleName. So, the column has been there for as long as I can remember and the only db changes we made to use the column was to actually pull it back and not just pull the RoleName back for the DisplayName column (why that was done in the first place, I don't know).
You're only seeing this problem when adding child sites, right? You haven't had it on new root sites all, correct?