Steps to replicate the issue:

• Turn live preview off
• Start editing a section that contains a transclusion (example)
• Click "Show preview"
• Confirm the section of the edit form that lists transclusions has "Templates used in this preview"
• Click "Preview" in the WikiEditor toolbar
• Wait a few seconds

What happens?:
The page says "Templates used in this section".

What should have happened instead?:
The page says "Templates used in this preview".

Other information:
When you edit an entire page, it says "Templates used on this page" and it changes to "Template used in this preview" after first preview. But since there is no table that records transclusions for each section, the list of transclusions within one section only is not available until only that section is parsed . So it makes more sense and is less misleading to always say "Template used in this preview" after any preview, be it an entire page or just a section, as "Templates used on this page" lists transclusions for the current (saved) version of the page.

"Templates used in this section" (templatesusedsection) is used when editing a section while "Show preview when starting to edit" is enabled.