Wikimedia Bugzilla is closed!

When the expanded contents of a template look like this:
[[Category:Foo]]
[[Category:Bar]]

The resulting HTML looks like:
<link rel="mw:WikiLink/Category" href="..." typeof="mw:Object/Template" about="#mwt1" data-mw="..."><span about="#mwt1">
</span><link rel="mw:WikiLink/Category" href="..." about="#mwt1">

(where the span wraps a newline)

This generally happens whenever a category is the first thing in the template. The first <link> node is a DOM node that represents both a template and a category at the same time, which is not something VE is equipped to deal with in a reasonable way. We could hack it such that it would, but in general one DOM node representing two different things at once is not something we like working with.

(CC Rob because he's affected by this)