BGP session initially comes up but after learning all the routes from the peer ODL stops sending BGP keepalives. So the peer drops the session with code 4 (hold timer expired). Then when BGP comes back up it gets stuck in "OpenConfirm" at the other end (as no keepalive received from ODL).

ODL claims it is sending keepalives:

2014-06-23 10:57:24.927 BST [nettyThreadgroupModule$NioEventLoopGroupCloseable-7-6] TRACE o.o.p.b.r.i.BGPMessageToByteEncoder - Encoding message: Keepalive [augmentation=[]]
2014-06-23 10:57:24.927 BST [nettyThreadgroupModule$NioEventLoopGroupCloseable-7-6] TRACE o.o.p.b.r.i.BGPMessageToByteEncoder - Encoded message:
2014-06-23 10:57:24.927 BST [nettyThreadgroupModule$NioEventLoopGroupCloseable-7-6] DEBUG o.o.p.b.r.i.BGPMessageToByteEncoder - Message sent to output: Keepalive [augmentation=[]]
2014-06-23 10:57:24.928 BST [nettyThreadgroupModule$NioEventLoopGroupCloseable-7-6] TRACE o.o.p.f.AbstractSessionNegotiator - Message Keepalive [augmentation=[]] sent to socket

but from a tcpdump and from debug on the router that's clearly not the case.