Update: this issue was addressed by Cumulative Update 6 for BizTalk Server 2010
Recently I was investigating an interesting problem in BizTalk Server 2010. All of the sudden events generated for receive locations just stopped being recorded. Noone has changed the configuration. For a simple messaging scenario, in which message flows from receive location A to a send port B, you could see the send port events being tracked. But no sign of when and where the message was received.