Unexpected series of messages from Digi Digital I/O Adapter

From
http://www.digi.com/wiki/developer/index.php/XBee_Digital_I/O_Adapter

“the ‘IC’ parameter is set to a mask indicating which I/O lines to monitor for a state change. Once the desired mask is set, any changes in logical state on the specified lines will generate a sensor reading …”

I used the IC command with mask 3D.DF. The digital sensor generally works, generating messages with a sensor reading different from the previous one, e.g. the coordinator receives:

Sun 11Jul2010 05:53:33 01.3D.DF.00.09.03
Sun 11Jul2010 05:53:27 01.3D.DF.00.08.03
Sun 11Jul2010 05:49:38 01.3D.DF.00.08.01
Sun 11Jul2010 05:49:33 01.3D.DF.00.08.03
Sat 10Jul2010 11:06:38 01.3D.DF.00.09.03
Sat 10Jul2010 11:06:32 01.3D.DF.00.01.03
Sat 10Jul2010 10:28:13 01.3D.DF.00.09.03

However sometimes the coordinator gets two or more messages with the same sensor reading, e.g.
Fri 09Jul2010 13:58:07 01.3D.DF.00.01.03
Fri 09Jul2010 13:58:06 01.3D.DF.00.01.03
Fri 09Jul2010 13:58:04 01.3D.DF.00.01.03

Based on the documentation I would never expect to get the same reading twice in a row. My fear is that I am missing some messages (states transitions) occurring in-between the successfully received messages. Has anyone seen this behavior in the Digital I/O Adapter or in the XBee Series 2 RF module (which is the core of the sensor)?