midi confuses (de)crescendo endings

[David Bobroff]

This is weird.  With LilyPond 2.1.29 the following code chokes and says:

 warning: can't find start of (de)crescendo:
    c-\
       !

But it still produces the correct output. (???)

If the \midi block is commented out it runs just fine.

-David

\score {\notes \relative c' { 
    c1-\<
    c-\!
 }
    
    \paper { }
    \midi { \tempo 4 = 60 }
}