How to set up a matrix in a UDO Form so it works like the Orders document lines matrix (new row/delete row with an ordered column)

We have designed a UDO form with a matrix linked to the UDO lines. We set the '#' tittle in the first column and set all columns to sortable="1"

In the item changed event we tried the datasource clear + matrix.add and other methods found in the forum so it adds a row with the new line number.

But we see there must be some missing step because in the Orders document when you have a new line and you order by a column, the new line is always at the bottom:

While in our Form´s matrix the new line is reordered with the other lines:

Also in our matrix the new line number is only set correctly by SAP when we add the first new line (line nº2) if we add a third line or more it is set automatically to 2 instead:

(we had to set the correct line number manually after adding the row, but we suppose it should work with the SAP automatic numbering like in the Orders matrix)

Thanks beforehand