Dual boot dirty bit problem

As a feasiblity test for a neighbor, I set up a Windows 7 + Windows 10 dual boot machine with each OS on different HDD's, intending to switch using BIOS boot menu. When I restarted I got a chkdsk message about corrupt drives - all partitons including system reserved seemed to have a problem. I clicked several times to cancel the check and everything worked OK, but obviously this isn't ideal.

The chkdsk problem didn't go away, so I let the checks/repair proceed and it found and corrected 1000's of 'errors'. Then I found the boot order had changed so the newest OS had priority regardless of BIOS setting. Chkdsk seemed to have screwed things up somehow.

I saw a solution online using cmd and ' chkntfs /x c: ' to reset the dirty bit, but the system reserved partitions don't have a letter. I know there's a standard way to dual boot, but I'm puzzled why my method doesn't work.

I seem to remember seeing this problem dual booting W8 and W7, but can't remember if I solved it.

Thanks guys. I disabled fast start in Windows 10 and in the BIOS - no more corrupt drive messages.

update : disabling fastboot in BIOS was not necessary in the end - just turning off fast start in Windows 10 was enough to stop the chkdsk error meassages.

Now my neighbor can use Windows 7 for general use, and experiment with Windows 10 until he gets used to it. Since the OS's were installed on different HDDs with their own system reserved, sometime in the future he can dispense with W7 and W10 will boot OK.

Point taken, although my last comment re BIOS was referring to after the big 10586 upgrade. I guess it's YMMV.

BTW on a different machine, the big update managed to break my hacked 'WMC/TV tuner on W10' malarkey, but I managed to get that fixed.