i encounter the same problem you described. I don't know if it has to do with the upgrade from 11414 to 11426 server side.
For testing i created a new simple qvw with a Button and a Chart without any data. I publishes the document via the server. I see only the chart. But if i minimize the Chart it disapears to i don't see the caption. It is still there but invisible. I see that because of the mouseover effect.
I attached screenshots.
Screenshot from the QV Client
Screenshot from the Browser Ajax
Screenshot from the browser minimized the chart.