Reproduction steps

I've observed this occurs in Firefox 67 and Chrome 73 on macOS, although in a couple of cases it seemed like I had to log out and log in again for it to work.

1. Enable the "New Wikitext Editor" beta feature
2. Attempt to manually open the VisualEditor in namespace where it's disabled by adding the query parameter veaction=edit to the URL (for example, navigating to https://en.wikipedia.org/wiki/Wikipedia:Requested_articles?veaction=edit)
3. Observe that the 2017 wikitext editor has opened, but the text area contains the page's raw Parsoid HTML rather than the wikitext. For example:
   

In T199411, @Schnark wrote:

The actual result depends on your settings:

1. If you have NWE enabled: You are editing the HTML (not the wikitext) in source mode.
2. If you never edited before: You are shown a welcoming dialog without any button to close.
3. If neither of the above: You edit in VE, but with a few bugs. E.g. when reviewing your changes there will be an additional loading bar that doesn't go away.