I am not a botanist, nor do I play one on the internet. But...

It looks like butter beans and lima beans are 2 distinct varieties, albeit
very similar. Most of the web sites I found when I googled "phaseolus
lunatus" didn't make a distinction, but
http://www.botanyworld.com/phaseolus.html is one link that does.

It wouldn't surprise me if some unscrupulous farmers passed off plain old
lima beans as butter beans (or vice versa) to unsuspecting canners :-)

I grew some lima beans in my garden this summer, they were delicious raw
(tasted very much like peas). They were so much better than the frozen
ones when cooked I couldn't believe it.

I also learned in my googling that wild lima beans (well, wild "phaseolus
lunatus" and possibly other variants) can be poisonous until cooked.

ScottR
--
Scott Robins