Hidden input is messing up grid - html

Question

I am using twitter bootstrap to style my admin panels, however this is very strange behavior. I've tested in Chrome 28 and Firefox and it messes up grid when I add a simple hidden input.
If you move hidden input into div.span6 or remove it completely it will work as intended, but if it stays there the rows collapse and do not work properly. By properly I mean that they should be next to each other, not on top.
Fiddle: http://jsfiddle.net/EZMvB/
<div class="container-fluid">
<form action="/admin/category/create" class="row-fluid" method="post">
<input type="hidden" name="WAT" value="WAT" />
<div class="span6">
<label for="NameEnglish">Name (English)</label>
<input class="input-block-level" name="NameEnglish" type="text">
</div>
<div class="span6">
<label for="NameEnglish">Name (English)</label>
<input class="input-block-level" name="NameEnglish" type="text">
</div>
<input type="submit" value="Create" class="btn btn-large btn-primary pull-right">
</form>
</div>

Answer 1

Putting class row-fluid in <form> tag in general is bad practice, because you always end up with one row, where as you could end up needing more then one row in your code.
Example here in jsFiddle
Code:
<form action="/admin/category/create" method="post" novalidate="novalidate">
<input type="hidden" />
<div class="row-fluid" >
<div class="span6">
<label for="NameEnglish">Name (English)</label>
<input class="input-block-level" data-val="true" data-val-required="'Name English' should not be empty." id="NameEnglish" name="NameEnglish" type="text" value="">
</div>
<div class="span6">
<label for="NameEnglish">Name (English)</label>
<input class="input-block-level" id="NameEnglish" name="NameEnglish" type="text" value="">
</div>
<input type="submit" value="Create" class="btn btn-large btn-primary pull-right">
</div>
</form>

Answer 2

Seems to work as desired if you move the hidden field (http://jsfiddle.net/EZMvB/1/). Not sure why placement matters since the default style of display: none should prevent it from affecting layout?
<div class="container-fluid">
<form action="/admin/category/create" class="row-fluid" method="post">
<div class="span6">
<label for="NameEnglish">Name (English)</label>
<input class="input-block-level" name="NameEnglish" type="text">
</div>
<div class="span6">
<label for="NameEnglish">Name (English)</label>
<input class="input-block-level" name="NameEnglish" type="text">
</div>
<input type="submit" value="Create" class="btn btn-large btn-primary pull-right">
<input type="hidden" name="WAT" value="WAT" />
</form>
</div>