In the font-family attribute of css, sans-serif is given precedence regardless of its position in the list

When sans-serif appears in the list of font families given in the font-family attribute of a css file it seems to take precedence over all other font families given regardless of its position.

Find attached a minimal code example that shows this problem.

In the example given sans-serif will be used regardless of its position in the list, while removing it yields the expected result, ie. the first font in the list is used.