[1] The Haskell 98 Report: Predefined Types and Classes
http://haskell.org/onlinereport/basic.html

This behaviour is not what I expect after reading the description at
http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:round
. Given that this behaviour has caused a bit of confusion I think a
change to the documention might be in order.

Given that the documentation says "round x returns the nearest integer to x", I think pretty much any behavior can be expected -- there's no single integer nearest to 2.5. The documentation certainly needs updated though.