Indeed, you shouldn't have this problem. Do you use a Ram manager? I use FreeRam XP Pro ( free), and though it isn't entirely reliable when displaying available RAM, it gives a good approxiamtion of the memory you have left ( as long as you're not  using the swap file for memory, then Free RamXP Pro is useless)
You would be able to see how much mlemory you have and see if it is normal or not. But I suspect is isn't normal anyway. Maybe you should open a support ticket at e-on's.
It's the first time I hear about your problem.