I don't understand a play

In the wordgame: http://littlegolem.net/jsp/game/game.jsp?gid=1732791on move 9, my opponent played outhouse, reversing the U (the second U of the word) from white to black.

Why did the computer change the U and not the T, which was the first white letter encountered.

Although the computer chooses be default the first letter to flip over, you may override that by clicking on a different letter.

"be default", of course, should be "by default".