Did it also happen if the focus in your VM switches to another app and then back to C::B ?
C::B checkss for changed files, if it gets activated.
If you switch away from the VM and change the file outside of it, it is the same as working on two machines and C::B most likely stays activated.
To change this behaviour, we would need to call the check-function in a timer-event, but this will slow down C::B .