Fullscreen issues with dedicated GPU on Laptop

[Ben]

Hardware: Lenovo P50, integrated graphics and dedicated NVIDIA graphics, using proprietary drivers.

Software: Ubuntu Mate 17.04

Issue: When running in the Intel integrated graphics mode to save power, the GPU and all the display ports wired to the GPU are disabled. Therefore, whenever I use external displays/need more power, I switch to the dedicated "performance" mode with the proprietary NVIDIA driver.

This results in fullscreen on the laptop's builtin display not working. Whenever you try to drag a window to the top of the screen on the laptop display, the preview shows it on the external display/it goes fullscreen on the external display, and when pressing the fullscreen button it automatically always becomes fullscreen on the external display. Same goes for fullscreen video, it all goes to the external display, not the builtin laptop display.

If needed, I can record/upload a video of the behavior so I can better explain it, let me know if there's anything I need to do, thanks!