This behaviour contradicts with description found in docs (in which
<source> tag specify interface in host, not in container). I think,
the previous bridge must be specified as
<interface type='bridge'>
<mac address='00:16:3e:34:21:9e'/>
- <source bridge='eth10'/>
+ <target dev='eth10'/>
</interface>

You are right. It is bug.

Well, here is the patch, that fixes that behaviour.

P.S. Are someone going to implement
      <interface type='bridge'>
         ...
<source bridge="...">
         ...
       </interface>
part of openvz driver? :)