mystery to the back of my mind. If anyone happens to understand this stuff, I'll sleep better once I've understood this.
I think it's another hardware bug, and I think the description as ramesh wrote it would be nice to have in the FAQ. One of these "set this bit, don't ask why" type situations.
Check for errata notes on the part. Perhaps the polarity of the enable/disable bit is flipped and incorrect in datasheet.