Dreamweaver converts UTF-8 files to ASCII

I have an issue where Dreamweaver 2021 converts UTF-8 encoded files into US-ASCII when it opens the files. Consequently, some symbols (e.g. ¥) get changed to garbage. 

The files are CakePHP CTP files. They don't have encoding meta at the start of the file (it's in a header file instead). I think DW uses the meta encoding tag to work out the encoding used to decide what format to use when opening the file. 

In Preferences, I have already set default encoding for new files to UTF-8, and also selected the option 'use when opening existing files that don't specify an encoding'.

Is there a way that I can make DW identify UTF-8 files correctly?