confirmed on:
Samsung Galaxy S4 (phone) Android 5.0.1
Samsung Galaxy S5 (phone) Android 5
LGE Nexus 5 Android 5

What I expected to happen if I cast anywhere that the bobber gets on fire, then the bobber would burn up and the fishing action would end (i.e. you could now cast a new line and bobber again, preferrably not into the fire). Maybe the rod would be damaged more than usual for my stupidity/entertainment.

What actually happened
I cast the bobber so it travels through the flames or lava and lands somewhere. The bobber catches fire and remains on fire until I retrieve it. After retrieval it is not on fire any more. If the bobber lands in water, it still burns forever (see pics) and you can even catch fish with the flaming bobber. If you land the bobber on land, nothing else seems to catch fire from the bobber.

You can cast into lava too and the bobber burns forever, but the bobber does not float on water.

By "bobber" I am referring to the red, white and black thingy on the business end of the fishing rod. Others call it a lure or bait. It looks like a bobber with a hook right on its end. So yeah.