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? :)