The Intel SSD 520 and 530 use SandForce controllers, so Intel started with a big mess and spent months trying to clean it up before shipping the drives. Clearly they missed a few bugs, and they couldn't work around every mistake and design limitation in the controller's hardware.
Intel's in-house designs have an extremely good track record. I'm only aware of two major bugs.
I don't know if this only affects the SATA SSDs or not, but it happens a lot. (BTW, the random disappearing also affects some other SSDs from other brands.)