As soon as I boot up when the KVM switch is attached, the resolution changes to 800 x 600. Unplugging the KVM switch and connecting direct to the keyboard/mouse/monitor, and it reverts back to the original settings.
Why does this happen?
Obviously, I have changed the resolution back to the original while the KVM switch is attached.
Have you installed a specific driver for your monitor, or are you using one of the "generic" drivers? I'd suggest using a specific driver, if one is available. Otherwise, at least make sure you have chosen your monitor from the list of supported monitors. Your video adapter driver may also have a setting to use or ignore DDC.
It sure looks to me like the problem is DDC, since it works fine when you hook-up the monitor directly. The KVM is not sending the DDC to the video adapter.