Why does my 2012 Retina Macbook Pro's trackpad become extremely unresponsive after I plug in a USB mouse? The only trackpad command that works is the left click, I can't select text or press down and hold the trackpad to do anything else until I restart.

My trackpad becomes REALLY unresponsive after I plug in a USB mouse. It seems like the cursor is broken and stuck on a permanent left click or something. I'm unable to select text or do any other sort of action that requires you to hold down the trackpad and drag. Mouse icons don't update as I scroll over different text and links. The trackpad is usually stuck in this unresponsive state until I restart my macbook which is extremely inconvenient if I have to do this after every time I use a USB mouse. Are there any fixes to this?