Missing section numbering when disabled and re-enabled

[xcoulon]

For example:

= A title
:sectnums!:

== Disclaimer

:sectnums:

== Section A

currently renders as

<div class="sect1">
<h2 id="_disclaimer">Disclaimer</h2>
<div class="sectionbody">
</div>
</div>
<div class="sect1">
<h2 id="_section_a">Section A</h2>
<div class="sectionbody">
</div>
</div>

instead of

<div class="sect1">
<h2 id="_disclaimer">Disclaimer</h2>
<div class="sectionbody">
</div>
</div>
<div class="sect1">
<h2 id="_section_a">1. Section A</h2>
<div class="sectionbody">
</div>
</div>