MC44: material usage value affected by factory calendar

Hi Gurus,

I've got the following problem: on my 4.6c R3 production instance factory calendar had been setup as 7 working days a week but recently the need was to change it to 5 working days a week due to the introduction of route calculation to determine correct dates for the sales orders.

We changed the factory calendar (which did deliver the correct result for the sales orders) only to discover that the "Usage" value determined for the materials by MC44 got totally wrong (usage with the 5 working days calendar was approximately 30 to 50% LESS than with the 7 days working calendar !!)

As soon as we did restore factory calendar back to 7 working days a week MC44 was again fine (obviously sales orders date got wrong...).

My impression is that everything is based on the way data from table MVER is determined depending on the factory calendar (which is apparently driven by function module DATE_CONVERT_TO_FACTORY_DATE).

I guess I could change from customizing the calendar for the shipping point: in that case my expectation is that sales orders date should be fine as well as results from MC44 but I'm not totally sure about that.

Any idea ? Do you know which is the way table MVER is populated based on the calendar settings ?

Many thanks in advance for your help.