Grub cannot write bootloader - Dell xps 14 Intel smart response

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http://askubuntu.com – I have a Dell xps 14 with dualboot windows 7 / ubuntu 12.10 on the windows side is active intel smart response ssd caching, while on the ubuntu side 11Gb ssd space is accessible as /dev/sdb1 . windows and ubuntu are installed in /dev/sda, while /dev/sdb is dedicated to caching and for bootloading. Now the nasty part: while caching is active, windows can modify /dev/sdb's mbr, while ubuntu cannot. funny thing is, no errors are reported by grub while doing a grub-install. Right now the only solution i found is to deactivate caching from windows, do my business on the mbr from ubuntu, and reac (HowTos)