How do I typeset this!?

[Matthias Berndt]

Hi, 

consider the following bit of markup:
\new Voice << { <e' a'>1~<e' a'>2 } { e''2. c''4} >>
It looks pretty straight forward to me, but Lilypond (2.11.23) doesn't 
manage to typeset this properly, the e''2. doesn't get a stem and I also 
get warnings telling me that a note head is being added to an 
incompatible stem. How can I fix this?

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