Icons stretched wide with "Internet Explorer"

On some Table instances in a Vaadin 7.3.10 app, I call “.setIcon” and passe a “ThemeResource” for a PNG image.

this.interchangeTable.setIcon( new ThemeResource( "icons/interchange.png" ) ); Works well in Mac browsers. Screenshot (in Retina resolution) – note the
shape of the green checkmark and blue flame

But in Internet Explorer 8 & 9, the
icons are stretched

In IE 8, the icons are always stretched. In IE 9 the icons are initially good, but if you hit the browser’s Reload button, the become stretched and stay that way.

Any idea what is causing this? Any workarounds?