code view: font size suddenly becomes illegible small

Again and again, when I use CTRL+S button to save my edits (when working in sourcecode window)  the text becomes suddenly extremely small and I cannot restore that. When I check my settings in Preferences the size of the Source Code Pro font (Unicode) is the same  as it was before (11 pt). But not in my window, it looks terribly small. I have to quit and restart Dreamweaver (Windows-version 21.6)  to make fonts look normal again. A shortkey bug perhaps? In my recollection it wasn't like this before.