Hello,
I have an UltraWebGrid that in the RowEditTemplate has two WebDateTimeEdit fields that are intended to be used to edit dates from the grid. They display the date successfully when the editor is brought up (although not in the correct format), however when I move the mouse over the boxes they clear and become blank input boxes. If I don't mouse over them and click OK the previous values are still retained, but once I mouse over them clicking OK will cause the data to be lost.
Take a look at the following Knowledge Base article that show how to use complex controls (non-inputs) in a row edit template:
http://devcenter.infragistics.com/Support/KnowledgeBaseArticle.aspx?ArticleID=5206
If you are doing something along these lines and the article does not resolve your issue, could you give some more information and maybe your aspx code?