Steps to reproduce (probably it can be reproduced more easily, but these steps work):
- Enable VE, NWE, and "Prompt me when entering a blank edit summary"
- Edit an article in VE, click "Save changes", enter a summary.
- Continue editing, switch to NWE.
- Change something, switch back to VE.
- Try to save.
Saving works without warning.
You are warned of a missing summary (though it is present).