Windows 7 multiboot issue

windows 7 keeps restarting when there is a hidden primary NTFS formatted partition
I assume it tries to install it's bootmanager there but is then unable to finish the installation

why is it that windows 7 can detect a hidden partition during installation and then decides to use it anyway even though it is hidden?

why is it so that any windows installation since NT4 overwrites the MBR by default and then fails to boot anything else besides MS operating systems?

I use grub to multiboot and therefore hide all other primary partitions upon selecting what OS I want to boot, that partition is then made active and unhidden.

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