Connections currently open count goes negative due to multiple calls to SelectChannelConnector.connectionClosed

Our application shows the stats as collected through Jetty re: connections etc. The connections currently open seems to stay around 0 alot, even though we know there's more connections than being reported.

Placing a breakpoint within SelectChannelConnector:937, shows the connectionsOpen was constantly hitting the check to see whether it had gone negative. The HttpConnection instance being passed in looked as though for some instances, two calls to close it were made - though both deriving from the SelectorManager.doSelect. Is this pointing at a larger issue?

SelectChannelConnector(AbstractConnector).connectionClosed(HttpConnection) line: 937
SelectChannelConnector.access$100(SelectChannelConnector, HttpConnection) line: 64
SelectChannelConnector$1.endPointClosed(SelectChannelEndPoint) line: 92
SelectChannelConnector$ConnectorEndPoint(SelectChannelEndPoint).doUpdateKey() line: 396
SelectorManager$SelectSet.doSelect() line: 370
SelectChannelConnector$1(SelectorManager).doSelect(int) line: 192
SelectChannelConnector.accept(int) line: 124
AbstractConnector$Acceptor.run() line: 707
QueuedThreadPool$PoolThread.run() line: 582