Suppose there is a module named "unstrip" with the contents

local p = {}
function p.unstrip(frame)
    return mw.text.nowiki(mw.text.unstripNoWiki(frame.args[1]))
end
return p

(the mw.text.nowiki is to keep the output from being expanded by the parser)

Calling this module normally works as expected, with {{#invoke:Unstrip|unstrip|<nowiki>foo</nowiki>}} generating "foo" as output.
However, if this is run through Special:ExpandTemplates, the strip marker doesn't get expanded, and the result is a strip marker `&#39;&#34;UNIQ--nowiki-00000000-QINU&#34;&#39;`