Wikimedia Bugzilla is closed!

Try out http://de.wikipedia.org/wiki/Spezial:Vorlagen_expandieren?generate_xml=1&input={{((}}Vorlage{{!}}X{{))}}

de.wikipedia has two templates, "((" expands to "{{" and "))" to "}}". When they are used on normal wiki pages, you are shown the braces as expected.
But in ExpandTemplates, while the xml tree is right, when the result is something parseable is will be expanded for the preview.

This behavior can also be found at http://de.wikipedia.org/wiki/Spezial:Vorlagen_expandieren?generate_xml=1&input=<p<includeonly/>re>X</pre>
Normally, nesting xmlishElements into another tag does not work (often used to insert includeonly tags at preloads), in ExpandTemplates it works for the preview.