Every one of those cases that I've seen has involved someone who knew that they were using a Monsanto product and were fully aware of the patents at hand. I'm not fond of Monsanto's practice, but the farmers were on shaky legal ground to start with.
In this case, one of Monsanto's (presumably patented) development products got out. I wonder if there's a case for invalidation based on negligent behavior allowing it out into the wild. Some level of doubt can be applied to products brought to market, but for those that never should have left a controlled environment, there may be other legal issues at hand.
I also wonder if there's not a chance of this being a random mutation. Does Monsanto put markers in its products that could be used to determine this?