Carpet placed over lava should catch fire pretty quickly, but it does not. If something else beside it catches fire, the carpet will burn, but otherwise, the carpet will not catch fire.

Steps to reproduce:

1. Create a structure like the screenshot.
2. Place the carpet over the lava by tapping the dirt block.
3. Observer that the carpet will not catch fire.
4. Place a plank or other flammable material beside the dirt block
5. Watch the plank and the carpet burn.

(Device: Asus Zenfone 5 Android 5.0)