If I tag an image while in the Preview window, the color management turns off. Untagging it, or toggling the "Manage Colors" button has no effect and the preview remains in the unmanaged state.
Rebooting PM seems to fix the issue for a while, but then it reverts to this behaviour.
Canon CR2 raw files, Photo Mechanic Version 6.0, build 3143 (3bc32e6), Mac 10.12.6