I Found IT!!!
OldRoses was right (and I was so wrong!) in that some people consider this plant to be invasive and in fact is is listed by Washington and Colorado as a noxious weed (although they do not go on to say why they are considered noxious). The reason they are considered invasive is because they self-sow so readily and their seeds can lay dormant for up to 50 years! I have been growing them in my garden for eight years and they have never been a problem. If I want to get rid of them it is as simple as grabbing them and giving them a yank. They aren't like dandelions or violets where if you don't get the whole root, the plant comes back.
I can only guess that perhaps how invasive they are depends on where you grow them. There are lots of garden plants that I find far more invasive (spiderwort, you know I'm talking to you!). This plant was not listed on Wisconsin's list of noxious or invasive weeds so I will happily keep enjoying these beautiful little flowers!