I had asked this before and you wanted me to build a sample to show what the problem is but while I was testing this out, I see where the problem is arising. For some reason, when you have a modal window and the grid is attached to it and the column is a calendar, the calendar becomes part of the modal conent. Meaning that you cannot select it like all other elements on the page. I think that this is what is causing the problem. As well, the calendar still does not show up in the front of the grid.
Does this help at all before I go an build a sample.
Thanks,
-Phil