Datagrid messing up combobox renderer

[sysnet]

I have a movie that use the Datagrid with a column displaying a combobox.
When used at _root level all seem to work ok.
But if I use it inside a function activated by a class that retrieve data from an ASP I have this problems:

a) The comboboxes appear blank (but if clicked it correctly show the item selected according to the content of the underlying cell).
b) If I resize a column (any column) the combobox of the selected row moves up or down randomly near the height of a row or disappears.

Any help?