Huge Memory Leak - HELPPPP

[FiFtHeLeMeNt80]

Hi;
I have a Windows server 2008 R2 Standard x64 with 24GB RAM as the HOST with two VMs :
1.Debian 6.0 x64 with 8GB of RAM
2.Windows server 2003 enterprise x64 with 4GB of RAM.

After 24 hours of running both VMs , I noticed 100% of my 24GB memory is used. but in the process list, there was no process that huge. so I suspected a memory leak in virtualbox.
As the next step I saved both VMs and noticed the memory is released and then started them , here is the result :

( it didnt allow me to post image here ! so I had to attach it to this post ! )

(1) I saved 8GB RAM VM
(2) I saved 4GB RAM VM
(3) I started 8GB RAM VM
(4) I started 4GB RAM VM

so you should compare (1) to (3) and (2) to (4). although both VMs had used more RAM before saving but the 4GB RAM VM which is windows had used around triple size of itself.
What can cause such a behavior ? The only related thing that I can think of is that I have checked "Use host IO Cache" in settings of both VMs and they are IO intensive.
I have attached the logs of both VMs. I would appreciate if someone can help regarding this matter because after start they are eating up all the memory so fast again

[FiFtHeLeMeNt80]

I have more information available. using RamMap tool from sysinternals I investigated the memory and it seems they are mapped files who are filling up the memory. look at the attached images.

[FiFtHeLeMeNt80]

As it turned out, it may not be a VB bug, it is windows 2008 issue ! more info : support [dot] microsoft [dot] com/kb/976618 ( forum doesnt allow me to post links yet )
But still the article says :

To work around this issue, use the GetSystemFileCacheSize API function and the SetSystemFileCacheSize API function to set the maximum or minimum size value for the working sets of the system file cache. The use of these functions is the only supported method to restrict the consumption of physical memory by the system file cache.

So may be the VB developers can limit the size of cache before it eats the whole memory. ( I know it is OS duty to take care of memory cache and etc, but it is Microsoft ! what do you expect ? )