Greetings, Lisandro!
This is the correct behavior. Some browsers crash when presented with multiple html editor boxes.
Here are three discussions that you might want to review:
http://moodle.org/mod/forum/discuss.php?d=89982
http://moodle.org/mod/forum/discuss.php?d=82635
http://moodle.org/mod/forum/discuss.php?d=81806
Perhaps you will find some helpful information in one of these.
atw
Quiz
WYSIWYG HTML editor not loading in essay
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