When you start/increase a workout program, it is pretty common for your muscles to retain water. It takes 3 water molecules to bond to each gylcogen molecule, and this helps deliver energy to your muscles more efficiently, and helps them cope better with the new demands you are making of them.
In the short term, this added muscle mass can lead to little or no change in the scale, even as you are burning fat. However, muscle and water are considerably denser than fat (check www.dailyspark.com/blog.asp?post=quiz_how_
for a great photo of this), and typically this shows up as lost inches. The tape is a often much more reliable measure of your progress than the scale. If you are losing inches, then you are burning fat.
It is possible to burn 800-1000 calories per hour, but you've got to be pretty fit and working hard to do this, and it is unlikely that you could sustain this rate for 2-3 hours. It is somewhat likely then that your calorie burn is an overestimate. How are you calculating this?
Also, if you open up too much of a calorie deficit, your body can attempt to close the gap by slowing your metabolism, sacrificing muscle to preserve fat stores and the like. This can actually hinder your long term weight loss efforts. If you are working out at anything like those levels, then it is important to eat to support that level of activity. You may want to update your Spark Exercise Goals (accessible from the LH side of the Start page) to more accurately reflect what you are burning (there is an option there to directly enter a weekly calorie target, rather than using Spark's minutes and days assumptions). Spark will use this to recalculate your recommended intake.
Finally, it is not necessary to work out at anything like that amount to lose weight. For most people, losing weight is 80% nutrition, and just 20% exercise. I would recommend cutting the amount of cardio workout time down to 30-60 minutes, and increasing the intensity of your exercise, and also using some of that time to include strength training.