What kind of stability should I expect from my mountain bike?

I had been riding my mountain bike, a '01 Stumpjumper FSR xc Pro, for over a year when I bought my '02 Litespeed Arenberg road bike. I immediately fell in love with my road bike and in less than a year have put over 3500 miles on it.

Although I still like riding singletrack on my mtb I spend nearly all of my time on my road bike now. One of the things that has impressed me most is it's stability. While some of my friends complain that their bikes become unstable during highspeed descents mine has always been rock steady.

Often when on long rides I will ride hands-free to rest my upper body. I also do it just because I can, but mostly because it's fun. Lately I've become even more confident and have been riding hands free up hills and around corners. My friends think I'm trying to show off but I do it because it just feels good to have this kind of confidence in my bike.

While my road bike is rock steady in stability my mountain bike on the other hand is not. After dusting off my mtb the other evening I took it for a quick ride on the road. I noticed very quickly that I could not even take my hands of the bars or it would try to squirm out from under me. Even after increasing the suspension pressure and the tire pressure it is still very unstable compared to my road bike.

Now this has me wondering; when compared to road bikes are all mountian bikes this unstable? Is it because it's a full suspension bike or are the hard tail's the same way? Could it be that my mtb just isn't the right one for me or have I just become spoiled to my road bike.

If I had the confidence in my mtb that I have in my road bike I believe I would start riding singletrack more often and probably be a better rider and have less injuries. What do you think?