Scheduling Assistance Missing when new proposed time received

Scenario when Scheduling Assistance Button is missing when new proposed time received:

1. Schedule a meeting with a colleague 
2. The colleague sends a new proposed time
3. You open the proposed time to accept the proposal 
4. You want to see or change time / date etc, but you do not see Schedule Assistance 

I've attached the image for reference, I've checked all menu options but i could not find this options appearing on my window, seems a bug.