PWM Duty Cycle Offset due to hardware limitation? NI-9472

Testing an NI-9472 using PWM code based on example found at link below. 

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000x1P0CAI&l=en-CA

Measured output appears to be indicating an offset in Duty Cycle timing that increases linearly as PWM frequency increases.   

NI-9472 has rated output rate of 100uS   

Testing appeared to indicate a 17% difference in commanded Duty Cycle at 1kHz Frequency, and roughly twice that at 2kHz.  

I believe this module should be capable of 10kHz output.  Is this kind of difference in measured Duty Cycle likely a limitation of the module's output rate? 

Any feedback very much appreciated!