I've finally identified the cause of intermittent errors with Flight Time (aka flight duration) and Fuel Burned information.
You must have your simulator's time, fuel and payload (and all other desired settings) set the way you want them before pressing the "Start Log" button on SPAACARS.
Once you press "Start Log" button on SPAACARS, any changes made to the aforementioned settings in you simulator will cause erroneous data in SPAACARS and ultimately uploaded with your pireps.
Now that this problem is identified, I will work on a new release to guard against this from being allowed to happen. In the mean time I request pilots to have their simulator's and aircraft set the way they want to fly BEFORE PRESSING THE 'START LOG' BUTTON.