But systemprofiler says it is ECC, too. So it must not only be the sticker (or bumper?) on it, but also the info stored in the chip.
But as you say that, it seems that it happens more than once, that people have the same Mainboards (Macs etc.), but see their Mac behave different.
For example, Macs with 128GB HDD limit. A member here recently reported he couldn't just use a 160GB drive and discard the rest that is over 128GB (me too), but others do that and it works fine. OK, that can be explained with different HDDs, brands, Firmware, etc.
There are other topics where reports for the same equipment differ. May it be, that there is a detail, we since now have overlooked. Maybe, we two have the exact same Board, but there is one single chip, that was manufactured by another sub-manufacturer and they were given differing drivers, firmware or whatever.
If, you were not living in the US, I would send you the RAM to let you test it in your board.