Comment # 33 on bug 1076779 from Ludwig Nussel

This is a special case I think. Here YaST creates a chroot for the purpose of
specially crafting an installation for the target system. So special measures
may need to be taken.

Anyways, another option would be to run the os-prober outside the chroot, ie
within the installation environment and only inject it's findings into the
target. Since /etc/grub.d/30_os-prober is quite expensive anyways, I'd favor
removing that and converting it into some standalone script that can be called
by e.g. YaST when needed rather than each bootloader update. Not sure if that
is doable short term though :-)