Going back to the zoom default setting is by design. The default setting for the monitor is 1680x1050. Press the Menu button to open the OSD menu and display the main menu. It must say Resolution 1680x1050 60Hz. if yours does not, then the video card display setting is incorrect.
After upgrading computers, I recently switched from using the DVI input on my SP2208WFP to using the HDMI input. I now have the same issue described by the OP. To confirm, the OSD says "Resolution 1680x1050 60Hz," but the Zoom is automatically reset to 10 after Power Save or changing any other setting on the OSD. With the Zoom at 10, part of the image is cut off, so it is annoying to have to reset the Zoom to 0 via the OSD any time Power Save is activated.
Zoom setting with HDMI reverts to 10 on reboot or power save. This was by design and never changed for this 7 year old monitor.
Purpose, no idea. That was a decision made by the manufacturer. I have never seen a way to bypass it.
* Open the Menu
* Click Factory Reset
* Click All Settings
* Go back to Positioning
* What is the default Factory Setting for Horizontal, Vertical, and Zoom?
I Have the same problem, interestingly, it only reared its ugly head 6 months after I started using this screen. I made adjustments on my Graphics Card Settings, made custom aspect ratio, reduced both sides to 85%. If you follow your GPU guides, you can adjust the computer, and let the Monitor act badly anyway.