If the target title argument contains a link from either another cross references or a regular external hyperlink, OurBigBook automatically prevents that link from rendering as a link when no explicit body is given.
This is done because nested links are illegal in HTML, and the result would be confusing.
This use case is most common when dealing with media such as images. For example in:
= afds


== qwer

{title=aa \x[zxcv][zxcv] \a[http://example.com][lolol] bb}

== zxcv
the \x[image-aa-zxcv-lolol-bb] renders something like:
<a href="#image-aa-zxcv-lolol-bb">aa zxcv lolol bb</a>
and not:
<a href="#image-aa-zxcv-lolol-bb">aa <a href="zxcv">zxcv</a> <a href="http://example.com">lolol</a> bb</a>
Live example:
This is a nice image: \x[image-aa-zxcv-lolol-bb].

{title=aa \x[cross-reference-title-link-removal][zxcv] \a[http://example.com][lolol] bb}
which renders as:
This is a nice image: Figure 21. "aa zxcv lolol bb".
Figure 21. aa zxcv lolol bb.