As all these Duals start off as Quads. It is not at all cost effetive to make Quads then disable half of it. If they are not defective they could sell them as Quads for exactly the same price, completly undermining intel's dual core range. They don't do this however as these chips do not meet AMDs own quality standards. Meaning that during testing these cores were found to fail under certain conditions. You may never be able to reproduce these failures in real life applications but it can be indicative of the quality of the chip.
By all means try it if you have a 550 X2 but don't ever buy one expecting it to unlock into a fully functional Quad core. And if you do unlock remember to test it thoroughly so that you are sure it is completely stable otherwise you will probably run into problems like the OP's.