In https://en.wikipedia.org/w/index.php?diff=prev&oldid=641792115 a template (but only one of them) got subst'd or turned into HTML or something:
{{citation needed|date= August 2014}}
became
<sup style="white-space:nowrap;" class="noprint Inline-Template Template-Fact">[<i>[[Wikipedia:Citation needed|<span class="" title="This claim needs references to reliable sources.<nowiki/> (August 2014)">citation needed</span>]]</i>]</sup>
This edit was done in Firefox 34 on Mac OS 10.8.5
Seems to be the same as T89163: Odd result: Subst'd template, or converted to HTML, or ???.
The DM html generated shows the problem here. The template consists of three children, the first two of which are categories. As categories are encoded as <link>s they are killed by the clipboard.
<link rel="mw:PageProp/Category" href="./Category:All_articles_with_unsourced_statements" about="#mwt286" typeof="mw:Transclusion" data-parsoid="{'stx':'simple','a':{'href':'./Category:All_articles_with_unsourced_statements'},'sa':{'href':'Category:All articles with unsourced statements'},'dsr':[50691,50725,null,null],'pi':[[{'k':'date','named':true,'spc':['','','','']}]]}" data-mw="{'parts':[{'template':{'target':{'wt':'citation needed','href':'./Template:Citation_needed'},'params':{'date':{'wt':'July 2013'}},'i':0}}]}">
<link rel="mw:PageProp/Category" href="./Category:Articles_with_unsourced_statements_from_July_2013" about="#mwt286" data-parsoid="{'stx':'simple','a':{'href':'./Category:Articles_with_unsourced_statements_from_July_2013'},'sa':{'href':'Category:Articles with unsourced statements from July 2013'}}">
<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;" about="#mwt286" data-parsoid="{'stx':'html'}">
<span typeof="mw:Entity">[</span><i data-parsoid="{'stx':'html'}">
<a rel="mw:WikiLink" href="./Wikipedia:Citation_needed" title="Wikipedia:Citation needed" data-parsoid="{'stx':'piped','a':{'href':'./Wikipedia:Citation_needed'},'sa':{'href':'Wikipedia:Citation needed'}}">
<span title="This claim needs references to reliable sources. (July 2013)" data-parsoid="{'stx':'html','a':{'title':'This claim needs references to reliable sources. (July 2013)'},'sa':{'title':'This claim needs references to reliable sources.<nowiki/> (July 2013)'},'dsr':[228,334,84,7]}">
citation needed
</span>
</a>
</i><span typeof="mw:Entity">]</span>
</sup>A separate problem is that the '<sup>' tag isn't getting a data-ve-ignore attribute, which is why we are seeing bad HTML, not just nothing. This is now T89658.
Change 190822 had a related patch set uploaded (by Esanders):
Fix clipboard DM for transclusion nodes starting with invisible tags
Change 190822 merged by jenkins-bot:
Fix clipboard DM for transclusion nodes starting with invisible tags