I spent a while this morning trying to figure out why I couldn't play “bidet”. It turned out that it was because the initial three tiles where “ide” and you aren't allowed to play a word which contains a previously played word.

Also, in WYPS, it wasn't clear to me on the first turn whether you are selecting the tiles for yourself or for your opponent. (I don't remember the wording, but I know that I mis-interpreted it. Luckily I don't think it made too much difference.)