Cross-staff slur spoils collision handling

[Urs Liska]

In my previous post
(http://lists.gnu.org/archive/html/lilypond-user/2017-01/msg00036.html)
I showed a complicated situation with a cross-staff voicing.

When I now add a cross-staff slur things get worse.

The red slur starts from the (upper) dis in the lower staff and ends at
a note in the upper staff. I can live with the issue that LilyPond
starts this slur above the upper staff, as I wouldn't expect software to
be able to properly find a way for this slur. But as soon as this slur
is present the vertical spacing is spoiled, and several elements overlap:

The blue accent is encoded with the upper dis in the lower staff (same
as the start of the slur), while the \f is in its own Dynamics context.
*With* the slur the whole lower staff is shifted somewhat upwards,
letting the accent and the dynamics collide. I have the impression is
actually the other way round: the collision handling is out of order,
thus allowing the systems to be moved closer together.
The colliding elements are placed identically when I force the slur down
(second image with the magenta slur).

So:

a)
Is it a (known) bug that adding a cross-staff slur negatively affects
collision handling?

b)
What element should I override to fix that collision with the least
hacky, semantically most "valid" trick?

Any ideas?
Thanks
Urs



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compound-slur-example-ravel-ondine-62.png
Description: PNG image

compound-slur-example-ravel-ondine-62.png
Description: PNG image