If a page has the following page settings added

__NOTOC__, __INDEX__,  or __NONEWSECTIONLINK__

then deleting headings will have <nowiki></nowiki> added to a page.

Example:

== Heading ==

=== sub-heading ===
__NOTOC__

And you delete all headings in VE, then <nowiki> </nowiki> will be added:

Deleting text or media do not produce <nowiki></nowiki> addition.