Observe:

Prelude> "a\nb" + ()

<interactive>:2:10:
    Couldn't match expected type ‘[Char]’ with actual type ‘()’
    In the second argument of ‘(+)’, namely ‘()’
    In the expression:
      "a\n\
      \b"
      + ()

Moreover, if “\n” is at the end of the string, it simply gets eaten:

Prelude> "a\n" + ()

<interactive>:3:9:
    Couldn't match expected type ‘[Char]’ with actual type ‘()’
    In the second argument of ‘(+)’, namely ‘()’
    In the expression: "a" + ()

It happens in GHC as well as GHCi. Tested on 7.8.3.