Weird table alignment override in website docs style

Now that I've pushed the first iteration of my planned reformatting
of function/operator tables [1], I notice that the table headings
are being laid out weirdly on the website. For example look at
Table 9.33 at

https://www.postgresql.org/docs/devel/functions-enum.html

You can see that the headings are being placed as though by
align=left, valign=bottom. This is directly contrary to
what it says in the XML source:

<thead>
<row>
<entry spanname="name" align="center" valign="middle" morerows="2">Function</entry>
<entry spanname="sig" align="center">Signature</entry>
</row>
<row>
<entry spanname="desc" align="center">Description</entry>
</row>
<row>
<entry spanname="example" align="center">Example</entry>
<entry spanname="exresult" align="center">Example Result</entry>
</row>
</thead>

Weirder yet, the default valign=top *does* seem to get applied
correctly in the table body; it's just the header that's wrong.

I poked around in the website stylesheets and couldn't spot anything
that seemed to be an intentional override of table alignment, so
I'm wondering if this is an artifact of the margins-hacking that
I do see there. Any ideas how to fix it?

regards, tom lane

[1] https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=e894c61836e4b967f7ec65358fdaed2ba86ed238