it IS a valid escape sequence. It doesn't have sense in that contex, you are right, but compiler doesn't care; It is a escape sequence, it mean ". return.
btw as you can see from the second bug (and i think you haven't read it to say so) this overflow is breaking some "good" code, so it is a ide's bug.
btw if the IDE's start to complain about the code you write, and not the compiler, I think there is something weird going on
edit: here the "other bug", just to be sure we are talking about the same thing http://code.google.com/p/arduino/issues/detail?id=962