jQuery Grid Plugin - jqGrid

I have a jqgrid with the datatype set to local.  The grid is being used for data entry, so we are dynamically adding rows to the grid.  The data behind those rows is a serialized object coming from the server through an ajax request.  I take the response from the ajax call and add the row to the grid.  When a user submits the page, we loop over the data in the grid, serialize it to a json string and post it back to the server.

My problem comes in when we pull the object out of the grid.  There are some properties missing, it looks like if we didn't define a colModel for specific properties jqgrid just ignores them and doesnt store them at all.   Has anyone else ran into this and/or has a workaround so whatever data we pass into the grid(whether it has a colModel definition or not) is exactly the same as the data we pull back out.

Here is an example of the call to add a row:

.addRowData(rowId, rowData, 'last')

Here is an example of the call to pull the row back out:

.jqGrid('getRowData', rowId)

Thanks in advance,

Kyle