Change of data type in the data panel is not doing a good job. Decimals from a database are imported as currency, and converting that to a number does not convert the underlying data type. Neither is it possible to convert text to numeric or numeric to text - its actually pretty useless for anything but geocoding.
Please see here... https://spotfireideas.tibco.com/ideas/TS-I-5612
my bad - already implmented. One just need to change it in the data panel itself