We need to gather some real facts before too long.
The UPS website indicates that in the recent years, the shipping regulations have been updated. Particularly for "Hazardous Materials" and liquified petroleum gas (butane, propane) such as our backpacking stove fuel falls squarely in that category. UN 1075 is that category(its on the canister, along with the DOT number for the container and the shipping restrictions and labeling).

The UPS website tells you a phone number for hazardous materials support as they have a Hazardous Material Support Center at 1(800)554-9964.

If you call be sure to have the UN 1075 number and the DOT number on the canister and be able to describe the container perhaps including the measurement of the diameter and the height and the container capacity.

The reason for this specificity is that the small 4 ounce canisters may fall under considerably different handling regulations than would the large 8 oz or larger canisters. Small pressurized containers are easier to design and prove safe than are larger ones. In addition, the explosions from their failure are smaller and less likely to outright kill someone or to damage the shipping vehicle or aircraft.

There are a variety of specific exemptions for liquid butane containers of less than one ounce capacity, for example.