Don't know if it's just me but I'm getting only one configuration entry when I print $event->payload.
For example if XML request is something like:
<event>
...
<payload>
...
<configuration>
<entry>
<key>domain1</key>
<value>foobar</value>
</entry>
<entry>
<key>domain2</key>
<value>foobar</value>
</entry>
</configuration>
</payload>
</event>
I get only entry with domain2 when I print $event->payload.