1.) std base frameless
2.) grow width to 48"
3.) S/P Editor -> add middle partition
4.) D/Dr Editor -> change settings for doors .4375 hinge side reveal
5.) add double doors to left section (door width is 11.75")
6.) add double doors to right section (door width of left section becomes 11.7813")
If you add a gap at the bottom of the Construction Settings dialog for the doors, then it should come out right. I used .125 gap and the doors came out to be 11.75 for all four.
The gap controls the gap between the double doors at the partition.
I think what John is getting at is that if you take the same 48" cabinet with a center partition and using the settings he describes, place a left hinge door on the left opening and a right hinge door on the right opening the doors size properly.
If you place a left hinge door on the left opening and double doors on the right opening the doors size properly
If you place a right hinge door on the right opening and double doors on the left opening the doors size properly.
If you place double doors on both openings there is a bug.
You can work around it by using the gap setting as you describe but that should not be necessary when working off a partition.
I have found through the years that the Gap settings are best set at 0 when your openings are all defined by partitions. It is best to set the all the reveals using the partitions. If you are placing multiple doors or drawers in a single opening then it becomes necessary to use the gap settings.
Many times I get cabinets from users where they have an entry for every gap setting and are trying to set reveals on a partition and don't get the result they are looking for. Usually it is a conflict with the gap settings.
This may not be the correct way of doing things but it gets consistent results. (unless there is a bug like John has found)