In 2017 WikiEditor, I went to a source editing page, located at https://en.wikipedia.org/w/index.php?title=V&veaction=editsource&action=edit or anything with `&veaction=editsource&action=edit`. I clicked a refresh button and/or pressed `F5`. The page switches back to one of old WikiEditors, depending on preferences.
If I enable the Enhanced Toolbar, after refreshing a source page in '17 WE, the mode temporarily switches back to the 2010 WikiEditor.
If I disable the Toolbars, after refreshing the source page in '17 WE, the mode temporarily switches back to 2003 WikiEditor.
In another scenario, I went a source page and then returned back to the article, the address bar went like this: https://en.wikipedia.org/w/index.php?title=V&action=edit or anything with `&action=edit`. Then I clicked the refresh/reload icon or pressed `F5`, and the mode switches me back to one of old WikiEditors.
This happens in most browsers that I've tested on, especially Firefox and Chrome. Nevertheless, the mode switches back to 2017 WikiEditor after exiting one of the old WikiEditors.