Order of definitions in source-highlight 2.10

I just upgraded source-highlight to 2.10 and I am noticing some strange 
behavior.

Suppose we have the file foo.lang:

symbol = "/"
comment start "//"

And the file test.foo:

// foo

The language definition is taken from the source-highlight manual, 
section 7.4: "Order of definitions".  Note that the definitions are in 
the wrong order, according to the manual: "The first expression will 
always be matched first, and the second expression will never be 
matched."  And yet:

$ source-highlight --lang-def=foo.lang -c foo.css --no-doc -i test.foo
<!-- Generator: GNU source-highlight 2.10
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span class="comment">// foo</span>
</tt></pre>

This was different with version 2.9:

$ source-highlight --lang-def=foo.lang -c foo.css --no-doc -i test.foo
<!-- Generator: GNU source-highlight 2.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><tt><span class="symbol">//</span><span class="normal"> foo</span>
</tt></pre>

What has changed between version 2.9 and 2.10?