Different time signatures on staves bug?

[Hajo Baess]

Hello all,

I need to typeset a lied (voice/piano) where temporarily the time
signatures change from 4/4 for both parts to 2/4 for the voice and to
6/8 for the piano and back to 4/4 again.
In the NR there is a nice example how to achieve this with equal
measure lenghts for the different time signatures.

I have tried to apply this model to my use case, but something does not
work as expected. The problem shows when you do not have have all the
same values in your last bar. In that case Lilypond only accepts less
than 6 crotchets there. Whatever I have tried with 

\set Staff.timeSignatureFraction = x/x

did not work, and I have no idea what is wrong here. To make things
worse: when I fiddle with the NR example and add a line with not all
the same values in 9/8, the same thing happens, too (see the added
third line there), and it even reacts to markup.

I hope that it is not a bug, but that I may have got something wrong.
But if it is one, the example is unusable as a global model.

Could someone here, please, with more experience than I have, help me?
Otherwise I am stuck with my project for the moment... I attach a
minimal example.

Thank you very much in advance

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