When publishing sections using Section Translation, sometimes the target section title is using the edit summary text as shown in the below screenshot

Additionally,
when a missing section is being published and no appendix sections exist for this article (in this case this section is positioned as "new", at the bottom of the page), the title of the section s replaced by the summary of the edit.

This is an expected behaviour, as per the Action API documentation (https://en.wikipedia.org/w/api.php?action=help&modules=edit), when when section=new and sectiontitle is not set, summary becomes the section title.