Bristlenose Pleco and companions

I recently purchased a lovely Bristlenose Pleco, about a month ago. He has gotten along with the Bulldog Pleco, and loaches thus far. Last week 2 of my 3 Ghost Shrimp disappeared. I blamed it on the loaches, even though they have never bothered the shrimp in the last year as tank mates. Today, however, I come home from work, and I witness my sweet Bristlenose trying to eat one of my prized female Mystery Snails.. She is partially closed, and Whiskers is digging at her like a child and an ice cream cone. I removed the snail, and will keep an eye on her in the Betta tank. My question is... is it possible for the Bristlenose to have eaten the shrimp (not a big deal), and is it normal for them to predate on Mystery Snails?

Poor snail. I am presuming that she was dead prior to the pleco's invasion, and her rotting body attracted him to her. He has not bothered my other female Mystery Snail, which is still thriving. She had an awful odor.. I suspect she was around 2 years old, as I had her for a year, and she was a good sized snail when I acquired her. I have kept 4 of her offspring, and still have another adult female, same age as the deceased snail, and my pretty male, who resides in his private bungalow..