IE7/8 and hover on empty elements

I had an annoying problem with IE8 today. In the CMS, toolbars appear when you hover over a content block or the page content. All I’ve done is user div:hover.

IE though does not recognise the object if its background is set to transparent and is empty. If you set a background colour then it fires the hover. I tried giving it hasLayout but that made no difference! Very strange behaviour!

Summary is: If you have an empty element where hover is not working, you need to give it a background colour!