URL: https://en.wikipedia.org/w/api.php?action=query&meta=siteinfo&siprop=specialpagealiases&format=xmlfm

Current response:

<?xml version="1.0"?>
<api servedby="srv214">

<error code="internal_api_error_MWException" info="Exception Caught: Internal error in ApiResult::setIndexedTagName: Bad parameter" xml:space="preserve" />

</api>

Seems related to the format parameter (specifically XML). &format=json and &format=jsonfm both work fine.

Discovered by Fran McCrory.

Version: unspecified
Severity: normal