Phased Submission of Approval Unit using Approval Groups

Summary:

We are trying to set phased submission of approval workflow for 2 set of accounts using approval groups feature.
While setting up the approval unit, we have selected the 'Extended Approval Flow' as 'Approval Groups' and also enabled the 'Phase Dependency' option.
As per documentation, the order in which the approval groups are present in the 'Assign Approval Group' tab will be honored for phased submission, and that the second group can't be promoted before the first group.
However this functionality doesn't seem to be working and we are able to promote and approve the second group before the first group is promoted.