hst:headContribution does not remove category in output

<hst:element var="jcaption" name="script">
<hst:attribute name="type">text/javascript</hst:attribute>
<hst:attribute name="src"><hst:link path="/js/jcaption.min.js" /></hst:attribute>
</hst:element>
<hst:headContribution keyHint="jcaption" element="${jcaption}" category="jsExternal"/>

results in
<script org.hippoecm.hst.container.head.element.contribution.hint.category="jsExternal" type="text/javascript" src="/site/js/jcaption.min.js"></script>

org.hippoecm.hst.container.head.element.contribution.hint.category is not a valid xhtml attribute for element script.