I'm assuming you're using GUID partitioning and an NTFS partition for Boot Camp. If that's not the case, this may not apply.
The Windows 10 installer makes changes to the GUID partition map. It installs a "protective MBR," a dummy MBR partition table intended to prevent old Microsoft disk utility programs that do not understand GUID from "seeing" the disk as unformatted and wiping it.
The changes that it makes to the GUID partition map are not part of the GUID spec, so Disk Utility does not recognize them. If you try to use Disk Utility to change the Windows partition after Windows 10 has modified it, Windows 10 will not be able to boot any more.
Edited by tacit (02/07/17 06:54 PM)