Placing text on multi-voice part

[Jogchum Reitsma]

Hi,

Noting
<<
  \new Voice {
    <<
      {
        \voiceOne
         a( \melisma bes c) \melismaEnd bes
      }
      \new Voice {
        \voiceTwo
         f2. f4
      }
    >>
    \oneVoice
   }
>>
 and corresponding text:

ste e --  lei --  son

I get the attached screenshot.

But I would expect (and want...) the text snippet "ste"placed on the 
three first quarter notes of the bar,  and the following "e" on the lat 
quarter.

The "lei -- son" then should be placed at the next bar.

What do I do wrong here?

Thanks in advance!

regards, Jogchum