Numeric text box property change executing on window close

I have a numeric text box that I would like to have update a database table when the property changes. the problem i am having is that when the window is closed the value in the table in the data base is updated to 0. this is the code i have in the propertyChange event.

if event.propertyName == 'floatValue':
	fpmi.db.runUpdateQuery("UPDATE table SET WtOF='"+str(event.source.floatValue)+"' WHERE RowNum = 1", "databasesource")

when i print out all the propertyNames when the window closes i see threadedProcessEnabled and ancestor. I am not sure whey the update statement would be executing on window close.

Is it running on window close? Or might something else be setting it to zero? Also, why don’t you use a bi-directional binding to achieve this functionality?