While I was looking into possible infections, I stuck to bacteria. I never really considered wild yeast. One abnormality that I hadn't mentioned yet is that the active, vigorous fermentation went on for an extra 2-3 days, at least. At the time I contributed it to low fermentation temps in my basement but extra yeast is a more reasonable explanation.
Considering the likely culprit, I can't defend my sanitation practices too vociferously, but I will say that my personality, and background as a biologist, doesn't really allow me to slack in that department. I've taken apart and thoroughly cleaned the spigot each time. I've also thoroughly cleaned the bucket with a rag and soap. With that said, I'll also admit there are always places to tighten up the program. The 90 degree corner at the bottom of the bucket is definitely a place that could get overlooked.
Regardless of everyone's success or horror stories related to plastic buckets, personally, I really like carboys for the simple fact that I can see what's going on. It fits my personality to see the whole process and in this particular instance, It would probably have clued me in to the problem.
