The "problem" is that my eMMC throws I/O errors and I use SDCARD as /home and MyDocs replacement.

/home automatically works correctly with SLOT_NUM /lib/udev/mmc_id trick as /dev/mmcblk0p2, but MyDocs /dev/mmcblk0p1 still gets detected as SDCARD during USB Mass Storage mode. Hence doesn't autounmount from N900