Simon Albrecht reported an ugly output problem here:

http://lists.gnu.org/archive/html/bug-lilypond/2013-03/msg00135.html

as follows:

Hello again,

one third contribution I have to make: in tight spacing situations combined with a clef change in another staff, slurs are oddly compressed or even, as in the example I added, reversed. Thanks for your excellent work and best regards

Simon Albrecht