did you run memtest for 9 days? because until the most recent release, that's how long proper testing took. You can not expect testing to work properly if you don't do it properly. Now it takes 4 passes...and it shows "1/4" when it starts. Then there's all these people complaining about how their ram doesn't pass the "Hammer" test, and how that's OK...actually... it's not.
9 days, seriously? Who's got that kind of time? That sounds really excessive and I've never seen that requirement stated anywhere. I've seen you talk about memtest before and I've not seen you say it before either, although I obviously don't see every comment you make lol, so I could have missed it.
Anyway, I ran mine for over 24 hours and on more than one occasion, along with various quickies and it passed every time. Dodgy sticks normally fail within a few minutes to hours, so 24 hours is pretty thorough. I also swapped the sticks round and fiddled with the BIOS memory settings, wiggled the modules with the computer running and generally faffed around quite a bit with it before giving up in frustration. If you're curious, the mobo was an Abit AN8 Ultra with the latest BIOS and not overclocked while I was testing.
I bought the RAM in February 2011 and ran the tests at the time, when it didn't work properly, so quite a long time ago as you can see. After not using the RAM for all those years, I then tried it in a different mobo belonging to my friend* a few months ago and that's when I discovered that one of the sticks wouldn't even let the PC post. Now, whether that stick degraded in the meantime or just works marginally on one mobo and not at all on another one I don't know, but I'm not bothered finding out as it's academic now. btw, he just bought some cheap and nasty HP prebuilt after that, which has very little upgrade potential, even though I said I'd help him put a PC together. Oh well.
*It was an Asus A8N-VM CSM. Yes, it was my mobo too until I gave it to my friend a few years ago to keep his PC building costs down as it was only for the common internet and email usage. Oh and I've got this PC back now, bought 4GB RAM for it the other day, plugged it in and it works. It's just that it reports that it's got 4GB RAM and 3GB useable in Windows 7 64-bit and the BIOS shows 3GB. Nice, lol. The manual of course says nothing about this problem. It runs well enough as it is, though.