I imported a Schema 4 XML project in Studio, since CafeTran Espresso 10 Croissant doesn't have a file definition for it.
I translated the project in CafeTran Espresso 10 Croissant and wanted to create a project TMX file for the client. So I chose Project > Export > TMX. The export file got the extension XML (and CafeTran Espresso 10 Croissant wanted to overwrite the XML that I had exported from Studio), instead of, correctly, TMX.
Small glitch, but anyway ...
CafeTran still appends the .tmx file extension even if the source file ends with .xml in the Save dialog.