The Filetype (used for syntax highlight) is reset after saving file. It would be nicer to retain the old filetype you manually selected.

Steps to repro:
* create a new file without extension
* type anything in any language. For example, type "echo 123" as if it were bash
* in Mousepad menu, click Document > Filetype > any language that highlights your text (for example, Scripts > sh)
* save the document

Expected at this point:
* your file is still highlighted with the filetype you selected

Actually: file type is reset from extension, which is plain text.