Ok, I got it!
The query is produced by a UNION, ans in one of the sub SELECTs, the column was
set to '0' instead of 0. This tiggered a converstion to text for the same column
in the next SELECT, probably in the ODBC driver, and this conversion implied the
use of a comma instead of a dot. For some unknown reason, it follows the rule for
French because the vesion of Windows is French, but bypasses the settings in