After a discussion with tammie, tested with firebug the input txt area to answer the "personnal question" test.
Firebug returns that the css used is signup_form.standard-form textarea line 347 in layout.css, wich is set at 90%
That is a problem if I set it on 50% no ? it will change other text areas and wont be fine huh ?
The "conflict" is that the text area is consequently too long and that it does not fit in the space given by registration page. (http://passion-cheval.net/register)
Not blocking but just confusing since the input text area is far from the question