If they're anything like my apple snails, they shouldn't touch the two plants that you mentioned. I have quite a few apple snails in my 55 gallon, and they only nibble on two different plants. They have eaten the riccia, which grows like a weed, and they have eaten some stargrass.
There's always sliced vegetables weighed down in the tank, so maybe this is the reason for them not touching other plants such as my anubias and java fern.