Fix in JCL 2.1.0-RC2.
When not in JposEntryRegistry mode then you can select under "Edit" - > "Editor mode" whether the editor should be in XML or Serialized.
If in XML mode then new files are saved as XML and editor will only load XML files. When mode is serialized then same but .cfg files.
Also, if the switch occurs while editing a file of the other mode then editor will ask to close the file.