When using it with a KVM it's not the USB -> PS/2 converter. It's that the KVM actually emulates the mouse and doesn't just switch it in and out as needed. Most machines don't like you hotplugging PS/2 devices so the KVM talks to your real mouse and then pretends to be one to the host computer. If the KVM doesn't know how to emulate the extra features on your mouse then you don't get it.