HTML click submit button twice
===

I recently added a CSS3 focus styling to a <textarea> element of a form (it grows vertically as to give more room to write). However, now when a user clicks the submit button, the textarea loses focus (and shrinks), but the form does not submit and the user must click submit again. Is there any solution to this?

 Form:

    <form name="postForm" id="post_form" onsubmit="return validate()" action="post.php" method="post" enctype="multipart/form-data">
	    <textarea name="post" onkeydown="update()" onkeyup="update()" placeholder='Write Post...' id="post_area" ></textarea>
		<div id='post_extras'>
		    <input class="admin_extra" id="post_button" type="submit" value="Post" />
			<input class="admin_extra" type="file" name="file" />
			<input class="admin_extra" placeholder="Image URL" type="url" name="url" />
			<div class="admin_extra" id='char_left'>5000 Characters Left</div>
		</div>
	</form>

CSS:

    #post_area{
	height: 3em;
	width: 100%;
	display: block;
	border: none;
	box-sizing: border-box;
	-moz-box-sizing:border-box;
	-webkit-box-sizing:border-box;
	padding: 10px;
	margin: 0;
	transition: height 1s;
	-moz-transition: height 1s;
	-webkit-transition: height 1s;
	-o-transition: height 1s;
    }

    #post_area:focus{
    	height: 10em;
    }

