https://en.wikipedia.beta.wmflabs.org/wiki/Page_previews_test_() has the wikitext:
(this text should be invisible) No other text should appear before or after this sentence (this should be invisible too)
Summary obtained via:
https://en.wikipedia.beta.wmflabs.org/api/rest_v1/page/summary/Page_previews_test_()
Expected:
Summary should be
<p>No other text should appear before or after this sentence</p>
Actual:
<p>(this text should be invisible) No other text should appear before or after this sentence</p>