Strange `interleave` element behaviour

[Maxim Taldykin]

Dear All,

I have this pipeline that will play two different files in left and
right audio channels:

    $ gst-launch                                                      \
        interleave name=i ! alsasink                                  \
        filesrc location=07.\ No\ Woman\,\ No\ Cry.mp3                \
            ! decodebin ! audioconvert ! "audio/x-raw-int,channels=1" \
            ! i.sink1                                                 \
        filesrc location=11.\ Sun\ Is\ Shining.mp3                    \
            ! decodebin ! audioconvert ! "audio/x-raw-int,channels=1" \
            ! i.sink0

It works fine, only one thing bothers me: sink1 goes before sink0. But
when I put them in order, it throws an error:

    $ gst-launch                                                      \
        interleave name=i ! alsasink                                  \
        filesrc location=07.\ No\ Woman\,\ No\ Cry.mp3                \
            ! decodebin ! audioconvert ! "audio/x-raw-int,channels=1" \
            ! i.sink0                                                 \
        filesrc location=11.\ Sun\ Is\ Shining.mp3                    \
            ! decodebin ! audioconvert ! "audio/x-raw-int,channels=1" \
            ! i.sink1

    WARNING: erroneous pipeline: could not link audioconvert0 to i

Why is it so? Is this a bug?

--
Maxim

The question is based on this one from SO:
http://stackoverflow.com/questions/8633381