I did not manage to use your structure. InDesign would add a Table>Cell structure, not allowing any intermediate tags.
However, I found a workaround to the described bug.
I would pre-create a large number of lines (more than the expected records of the database, which are supposed to be exported to XML)
Then, at XML import, I delete useless extra elements.
At the end, I get the expected result, with just the required number of lines in the table.
Thanks anyway !