To reproduce:

Go to a blank VisualEditor page, click edit, change entry mode to Heading 1 (or whichever Heading mode), select all (Ctrl-A or Cmd-A), type in some content, press 'Return'.

The content will appear (subject to bug 39517), but the 'Return' will cause the cursor to move to the left rather than inserting a newline. Indeed, further 'Returns' will insert newlines only to split a Heading, or when transitioning to a Paragraph or Pre-formatted block.

Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=39517