HTML: Missing image resource has strange effect on ToolTip

I hope someone can help me since I have no clue whats going on here. I have a table with an image in each row (at the beginning). Each image has tooltip (title attibute). HTML looks lie this:

<td align="center"> 
<input type="hidden" value="0" />开发者_运维百科;
<img src="/img/prognosis/2green.png" title="Augsburg-Göggingen ">   
</td>

To make the table sortable I added a hidden input with a value, that is the criteria for sorting.

Everything looks fine until I delete the .png file. Then it looks like this:

The grey rectangle's width is dependant on the tooltip's length. How can this happen? Any help appreciated! THX!

That's strange, what OS / browser are you using? A valid image should have an alt attribute, like <img src="img.png" alt="" />.
It looks like you're using XHTML, but your img tag is not properly closed.