Yes, it's normal. That's why you want "safe" plants in your enclosure. Some believe that it means your chameleon wants more water. You might want to look at your hydration to see if it needs to be improved, but it's normal for them to chomp the plants.
Oh yeah they'll eat dead leafs from time to time as part of their diet. My panther would nibble on the bark and dead leafs of my bay leaf bush. I freaked out at first but he's done it since he was 3 months old and seems strong and healthy so I let nature take it's course.