Hello Jean-Marc,
Update table will generate a new table if the number of columns has changed between the source table with the update table script, and the table in the database. In your case, because you have created formula columns this will be flagged as a difference, and a new table will be generated.
Because of feedback like this, JMP 12.1 and beyond will update the table in place IF the only difference are formula columns, and IF those formula columns are all at the end (rightmost) in the column list.
Brian Corcoran
JMP Development