WTF: robbing property difficulty

I'm fairly certain this has been happening, and that I've heard people saying this before, and my friend David R. mentioned it again this morning in one of our groups.

This was David's screen shot. He noticed a difference with at least three properties when he shot this.

I decided to do a little robbing to check it out for myself with a Rob Squad (I do farrr more fighting than robbing). Here is my after shot; compare it to the Before shot at the top of this post, and you'll see that the medium property that I have circled is the ONLY property whose difficulty level didn't change.

Is this a graphical issue, or is the property difficulty actually changing on us?