Dynamics and Lyrics don't mix

[Roman Stawski]

Hi folks

When I build the snippet

-----
\version "2.13.11"
\paper{ ragged-right = ##t }

<<
  \new Staff \new Voice = "a" \relative c'' { a b c d }
  \new Dynamics { s4\p s\< s\! s\mf }
  \new Lyrics { \lyricsto "a" \lyricmode { a b c d }}
>>
-----

the output is as expected, but I get a whole cascade of warnings

    warning: staff-affinities should only decrease

Can anyone translate this into English ? and/or tell me how to do to get
shot of them?

Inversing the dynamics and lyrics gets rid of the warnings. But doesn't
give me the output I want.


Thanks for any pointers

Roman