I got my share of Ram instability and a bad ram can hold even 3 runs of memtest86+ and fail at 5th or 10th. Or motherboard just won't like rams even if they are in QVL list.
Here's a story
I got my mobo+ram+cpu from the same place. These g.skill rams are a bit tricky. 1.6-1.65v for 8-9-8-24-2t 1866mhz. Now it was nightmare in first month. I couldn't get memory stable. Everything on stock. It BSODed, then could go for 2 days, then BSOD again. VGA driver would recover while gaming. IE and Catalyst would crash immediately after clicking them. CCC.exe, iexplore.exe and event viewer would crash too. I would have lotsa windows services crash logs on event viewer.
I found a trick, when I turn the computer off, and switch the psu off so mobo has no power, then wait for 30 seconds then power everything on again, the memory is stable. Remind you, when it's NOT stable, it would give lotsa errors on memtest, even with 1.7v, even with 1.2v VCCIO, even at 1333 or 1600 with 11-11-11-38 or combination of those. However when it's stable, it doesn't give any memtest errors at rated settings.
Then mobo died. Realtek ethernet port and usb 2.0 ports did not work and 2 days after, it started to stuck at VGA led meaning can't recognize gfx card. There's no advanced RMA here so I went with a regular rma and bought a Gigabyte Z68AP-D3(as a backup
) with the microssd slot
Now this is interesting. It had no problem with those g.skill memory. I had already created 2 partitions on my 500gb Caviar black, 90gb os partition so format was easy. However I did NOT reformat/reinstall Windows after mobo change. It had zero problems with memory on windows or memtest. I just selected XMP profile and bang, it just worked. Well ofc this gigabyte board is not for overclocking much, it lacks alot against ASUS p67 evo.
Then Asus p8p67 evo came back from RMA as repaired (not replaced) We don't have advanced RMA here but Asus has a good lab. They probably replaced some chips on the mobo and flashed a different bios. I tried it at weekend, reinstalling windows 7 this time and I could say, the board got a lot more stable. Now I rarely get MEmory Management bsod. Funny thing is immediately after a BSOD reset, memtest gives no errors
So to sum it up, it's not always Rams, sometimes otherwise a stable motherboard can go unstable with a non-faulty memory just because they don't like each other