https://bugs.freedesktop.org/show_bug.cgi?id=63579
--- Comment #10 from Erik Faye-Lund kusmabite@gmail.com --- Another data-point: My AMD driver also does not support line continuation characters by default, although they do *after* a "#version 420" line.
So in conclusion, I think blindly supporting line-continuation without a "#version 420"-line is both in violation of the spec as well as diverging from other implementations in a way that can only create problems.