nods said..
burning treated pine/old pallets is dangerous....they give of arsenic gas.
I don't think any pine pallets are made from treated pine. It's all just ordinary cheap untreated rubbish pine.
The reason is, they only last a few years so there is no need to treat against white ants or wood rot.
So,.. generally safe to burn.
The reason it stinks is that it is generally green pine, so lots of sap and high moisture content.
Pine poles and treated structural pine is not safe to burn. Do not burn for the reason stated above.
You will gas yourself and maybe others.