Textarea and Genshi

[Asmodai]

Hello,
I have one little question about TextareaField render (in tw.forms).
When i'm displaying empty form, (x)html code looks like:
<textarea id="description" name="description" class="required
textarea" rows="7" cols="50"></textarea>
But when i submit form (with empty field) textarea field looks that:
<textarea id="description" name="description" class="has_error
required textarea" rows="7" cols="50"/>
As you can presume Textarea eats rest of page in this case. I don't
know reason of this strange render behaviour but i think rendering
this as <textarea></textarea> is more secure for (x)html.
I'm using tw.forms-0.9.2, ToscaWidgets-0.9.3, FormEncode-1.0.1.
Here is my field declaration:
description = forms.TextArea(
label_text=u"Description",
validator = UnicodeString(not_empty=True)
)