I have seen the same thing as vincelwin.
When you have multiple deployments with different boot images deployed to a computer and PXE boot, it choose one boot image. If you then select a task sequence with a different boot image, it will restart your computer and load into that boot image. But this is not 100% safe there is no guarnatee the first boot image have the correct drivers for the specific model you want to deploy
Do anyone know what criteria SCCM / WDS choses which boot image to use with multiple deployments?