13" (2010) MacBook Pro Display settings are showing a second "built-in" display that doesn't exist

I have a 13" mid-2010 MacBook Pro, running OS X 10.10.2

I also have an LG 23MP75 monitor attached, at a resolution of 1920 x 1080 (60Hz) using the display port to a VGA adapter. This is my standard configuration for in the office.

When I attached my laptop this morning, and logged in to my user id, my monitor wasn't in it's normal "location" -- that is, I couldn't drag the cursor to the left off my laptop desktop and onto the second monitor. I opened up my System settings and discovered the most unusual monitor configuration I've seen...

What makes it unusual is that I don't have a third monitor attached.

The left-most screen is my laptop, the right-most screen is my external display, and the centre "screen" shows as a "Built-in Display" at 1536 x 2048 resolution.

I have unplugged and re-plugged the display adapter; I have detected displays (with and without the external monitor attached). I haven't yet rebooted (as I wanted to get screen shots in case the problem "goes away.") and the centre display persists.

I can rearrange the displays, and put the external back to where I normally have it, but that ghost display still sits there.

I have had minor problems in the past, when I switch from my external monitor to a projector and then come back to my monitor - the MacBook doesn't always remember the screen resolution and I've had to Detect Displays, and sometimes reset the resolution manually. But it's a minor issue; given that I'm swapping external devices in and out while my computer is asleep, it doesn't surprise me.

I have used iScreen in the past to extend my desktop onto my iPad, but the iScreen preference is currently turned off AND I'm not using my iPad, nor is it currently on the same wifi network as my laptop (on a hunch, I turned off my wifi, but the ghost display persisted).

Two questions:

1) Where did this "ghost display" come from?

2) More importantly, how do I get rid of it?