\partcombine in 2.6.4

[Frédéric Bron]

In the following example, "Solo" should be written above the first note. 
Note that if the crescendo is removed, everything is fine.

\version "2.6.4"
\include "english.ly"
\score {
       \partcombine
       {
               r4 c'\< r d'
               e'\!\f
       }
       {
               R1*1
               c'4\f
       }
}