Its not that they deliberately de-root plants they just dig in the gravel alot so none of the roots will stay buried. You can probably get around this with potted plants. Ive heard some people have good luck this way.
when I had my green terror a few years ago (who dug a LOT) it was suggested that if I wanted to keep live plants that I needed to have a nice deep substrate (2-3" deep) and bury the roots down pretty low so they woudln't be easy to dig up. hard to say if it would have worked (I didn't get live plants), but I know my terror used to dig all the time and would even take my cloth plants and drag them aroudn the tank!
You can get around the digging by placing stones around the base of rooted plants. Just be careful not to crush or damage the plant's stems/crown. Another alternative is to pot your plants...otherwise, stick to plastic plants.