Grid cell editors not working in IE9

The grids on my site use both text and combo cell editors. They all work great in Chrome and Firefox, but not at all in IE9. Double-clicking on a cell containing one of these editors does nothing, as if they are read only. Obviously this is a big problem. Any ideas on what is causing this? I was surprised to not find reference to this problem anywhere.

What version of dhtmlxGrid do you have?