Overwriting file with extension not registered in the file system but present in the Extensions Filter ComboBox might result in duplication of the extension in the resulting FileName. For example you have empty.stp file on your desktop. Choose the file with SaveFileDialog , chose the STP file extenion in the Filter combo box. Press Save. The resulting FileName of the dialog will be empty.stp.stp but it should be empty.stp. Available in LIB Version 2017.3.1225.