It is found that when using a custom editor (in my case a Kendo dropdown menu), the dirty flag sometimes disappears even though the cell and model are still considered 'dirty'.
This behavor is reproducible using your demo (http://demos.kendoui.com/web/grid/editing-custom.html). Follow the steps to view the error:
- Select a different value under Category for a row
- Select the Product Name cell in the same row (a different row will also work) to enable edit mode
- Click back to the dirty Category cell
- Click off to close cell
The dirty flag in the cell is now gone. The same behavor is happening with my implementation even though I have not saved the current grid. If you press "Cancel", the value is returned to the original.