Md5sum Fails In 10.3 X86_64

1. I installed 4 additional gigabytes of memory to my 2 and thoroughly tested it. I downloaded 10.3 x86_64 DVD and checked md5. I burned the image and verified it in the burner software. I verified the media in 32-bit SUSE, it is OK. I started the installation but the installer says bad media.

2.I downloaded CD instead and verified it (again 10.3 x86_64). Installer says OK. I install it, no complains.

Now the problem: When I calculate md5sum of the DVD image I mentioned before, it gives me different answer every time, occasionally giving the right answer. To eliminate caching I used two copies of the same image, both verified and calculated md5sum on them in turns.
Again, there is nothing like this in 32-bit version, it is simply rock-solid.

Playing with BIOS did not help (asus p5b-plus, latest bios)

Any help is appreciated

Update:

I reinstalled x64 again and applied all updates: no change

I removed 2GB of memory, leaving 4GB in two pieces: everything came back to normal. md5sum gives the right answer every time under the same conditions as before.

What is it? Is it a faulty kernel driver that does not know how to cross the 4gb boundary of bios giving a wrong memory map? Or perhaps two different kinds of memory? I ran memtest86+ for hours.