About your first issue, please make sure that you haven't made the grid to be open in edit mode initially in PreRender event or any. Check your code once more, if not able to resolve, provide your full code snippet. I'm not sure where you want to display the number of sub records, please try the following code snippet to get the number of sub records and display it along with the ExpandColumn.
You were right regarding first question! Somehow code i copied from Telerik demo contained code on PreRender. I removed it and all set now.
Code you provide for second question was interesting solution, but didn't work for all cases. Regardless i solved it with some sql.