documentation for nub and nubBy should be corrected, extended or removed.
While working on a fun math/programming exercise I discovered a peculiar behavior in "nub". While it worked the vast majority of the time, there were a few cases where it failed to purge all duplicates as defined by (==). Replacing the use of "nub" with "nubBy (==)" correctly purged all cases.
I have linked a codepad evaluation that outputs the strange behavior: http://codepad.org/VNauTAam
I would have isolated the bug better for you, but like I say nub works by far the majority of the time. This must be a peculiar clash with my custom data structures and strange definition of (==).