Propane has a much higher BTU per cubic foot of gas than natural gas, and runs at a different pressure. Consequently, the burner orifice (where the gas comes out and burns) is smaller for a propane burner than for a natural gas burner. If you take a stove that was designed for natural gas (i.e., a bigger burner orifice) and install it in a house that heats with propane, you will be cooking on great balls of fire. Gas stoves can be adapted back and forth between propane and natural gas by changing the burner orifices, but this one obviously was not.
In additional to all the above, propane also requires a different air-to-fuel ratio than natural gas to burn properly.
With the wrong orifice you get incomplete combustion, the orange flames you see in the picture. This may soot up the bottom of your pots and pans and also releases a large amount of CO which is obviously not a good thing.