Yes Kuhmann, this was somehow what I meant.
If the win partitions are both bootable one then one of them has go sleep for that moment, this will do the bootmanager.
For Linux it seems not to be important wheater the partitions are hidden or not. I have 3 bootable partitions with win and linux in the extended in a logic grive. Linux can access all the bootable partition hidden or not.
Just the bootmanager does not leave two bootable win partitions active. it will rather active the one which is selected on boot and hidethen the rest.