Why quest echoes are separate for each party member?

I was progressing mono in a party. Progress is shared, we both received stability and both advanced to the next mono after boss kill. However, we had to complete two quests echoes before the boss individually, every party member had to start and complete his own quest. Also when such quest is in progress, other players cannot start their own echos, error 62 is shown.
So in a party of two players we had to spend twice the time to complete quest echos. Party of 4 will have to do the same quests 4 times.
The right play in this situation would be to disband a party, complete quests individually, and gather the party back. That is odd and inconvenient.
Is there a reason for quest echos progression to be separated or is it a bug? Boss kill is shared among all party members, as long as they have stability, so there should not be a problem.

Moved to bug reports