You run a Transaction Integrator transaction for which the Conversion Behavior option of Always Check For Null is set to True. If padded strings are being sent in this situation, the transaction works as expected for some time, but suddenly the transaction starts to return incorrect results.
This problem occurs because the data is not packed correctly under certain timing conditions.
Cumulative update information
The fix that resolves this problem is included in Cumulative Update 1 for Host Integration Server 2013.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.