Cursor freeze in upper left when usb keyboard is unplugged

Bought a Logitech MX S bluetooth keyboard, because I need backlighting. I use a Logi m510 mouse. Both work perfectly — as long as the Apple USB keyboard is plugged in. Unplug the old kb, and the cursor freezes. It just seems weird that the only way I can use the computer is with BOTH the old usb kb plugged in AND the new bluetooth kb paired. I tried restarting in safe mode; no help. Reset pram. No help.