Strange end-of-line slur fragment (LilyPond 2.18)

[Urs Liska]

Hi all,

I'm entering a piece which has to be rendered with LilyPond 2.18, and 
I'm experiencing something strange with a broken tie/slur combination.

The code is:

    r8 f, as c f as c f (
    % (line break is here)
    f4

And the result is the attached one. The slur fragment before the line 
break is completely wrong, the second sibling works well.

Any idea what is causing this? And what would be the most 
straightforward workaround/fix (as said: in 2.18)?

Thanks
Urs

broken-slur.png
Description: PNG image