spacer rests and/or \sustainOff don't work as expected

[Werner]

I want to create a sustain-pedal-signature longer then the last note, because
other voice still plays. The code:

\cadenzaOn
r8 
\set Staff.pedalSustainStyle = #'mixed
e,8\sustainOn
gis ais c d e fis gis ais
\repeat unfold 9 s8
\sustainOff
\cadenzaOff

gives on the one hand nine error messages (I suppose for every rest) („don't
find a start for pedal“ or something like that) and on the other hand makes the
pedal-spaner end with the last note instead of the last rest.

Its independent of wrinting rest or spacer rest.

Without the repeat it's a little bit better:

\cadenzaOn
r8 
\set Staff.pedalSustainStyle = #'mixed
e,8\sustainOn
gis ais c d e fis gis ais
s1 s8
% r1 r8
\sustainOff
\cadenzaOff

This works fine with rests but doesn't work with spacer rests.

In my eyes this is misbehavior.

Is this considered a bug?
Would somebody change it in a way, that the second example works with rests and
with spacer rests?

Also the trick to make a sustain-spanner just a bit longer writing
\grace s2 \sustainOff
doesn't work. Spacer rests obviously aren't considered to be able to be grace
notes. So this s2 even causes bar-checking error. I would prefer, if spacer rest
would be accepted as grace-notes and as referenc-point for \sustainOff.

Greetings

Werner