How to determine Milestone automatic confirmation case based on its offsetting

Hello Experts

I'm having a problem with the milestone automatic confirmation logic and I hope you can help in solving this dilemma.

We are integrating PS milestones with SD billing plan in a milestone billing scenario. Whenever I confirm the holding activity of a milestone (any kind of confirmation) it automatically confirms all the subordinate milestones regardless of their offsetting "Offset to Start/ Offset to Finish/ Manual Offset"

Example:

I have an activity that holds a sales milestone which is offset to finish and aligned to earliest dates.

The activity's earliest start is 01/11/2015 and earliest finish is 15/12/2015.

Which means that the milestone's scheduled date is 15/12/2015.

Comes 1st of Nov. and we start the activity, we partially confirm the activity with minimal work and only one day of work (to keep track of actual dates).

The partial confirmation should not affect the milestone (since the milestone is offset to finish and a partial confirmation indicates anything but the activity's completion), However, the system behavior is to confirm the milestone regardless of its offsetting.

The system uses the finish date of the confirmation as the milestone date also regardless of the milestone offsetting.

Automatically confirming the milestone in PS (with actual date) removes the billing block from the relevant billing plan line in the sales document. Which in turn allows customer billing before its real due date and this causes a problem.

Do you have any ideas how to fix this?

Please see the first comment for the required behavior if anyone can help.

Thank you