Consider the following scenario:
You install BizTalk Server 2010 Cumulative Update 8 (CU8) on both BizTalk Server and MQSeries Server.
You use MQSeries adapter on BizTalk Server with ordered delivery enabled.
You enable multiple ports at the same time to process lots of messages, for example 20000 or 50000 messages.
In this scenario, you may receive out of order messages.
Cumulative update information
This issue was first fixed in the following cumulative update of BizTalk Server:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For information about the service packs and cumulative update list for BizTalk Server, see KB 2555976: Service pack and cumulative update list for BizTalk Server.
For more information about BizTalk Server hotfixes, see KB 2003907: Information about BizTalk hotfixes and cumulative update support.