Impossible or ambiguous (de)crescendo in MIDI.

[Graham King]

I'm trying to eradicate numerous "Impossible or ambiguous (de)crescendo in MIDI" errors from a large score, and two problems arise:

1) I'm finding it hard to locate the source of these errors.  So far, I've tried:

• searching the source for all dynamic changes ending with \! and converting this to -\omit\mf (or some other suitable dynamic;
• then sort-of-bisecting the problem by suppressing each part in turn,
• then visually inspecting the source for unterminated crescendos and decrescendos.

But it is still not easy to run the errors to ground.
Is there some better tactic for locating their cause?  (I note some previous discussion on this list[1], and issue 3945[2])

2) The second problem arose when I finally tracked down one such error.  Here's the minimal example:
>     \version "2.19.35"
>     
>     music = \relative {
>       c''2\p\< c |
>       c1\fz\>%-\omit\mf |
>       c\p  |
>     }
>     
>     \score {
>       \music
>     }
>     
>     \score {
>       \music
>       \midi {}
>     }

As it stands, this gives two of these error messages.  If I try to suppress them by uncommenting "-\omit/mf" I get the following errors in addition:
>     5:10: warning: Two simultaneous absolute-dynamic events, junking this one
>       c1\fz\>
>              -\omit\mf |
>     5:5: warning: Previous absolute-dynamic event here
>       c1
>         \fz\>-\omit\mf |
Is there a magic spell to soothe lilypond in these circumstances?  It might seem like nit-picking, but there are so many of these errors in the score that they are obscuring other, more important, messages.

Notes:
[1] For example, https://lists.gnu.org/archive/html/lilypond-user/2014-05/msg00648.html
{2} At the time of writing, this may be found at https://sourceforge.net/p/testlilyissues/issues/3945/