SWFmill Simple rejected 4-bit IMA-ADPCM WAVE file

[nachanon]

I have used SWFmill (simple mode) to create a SWF file from 4-bit IMA-ADPCM-encoded RIFF WAVE (.wav) file. As this codec is supported natively in SWF format, it should work.

But instead, SWFmill complained that it does not recognize the codec and its fmt chunk:

$ swfmill simple imaadpcm4play-stereo.xml imaadpcm4play-stereo.lib.swf
Error: Format code in WAVE file is not PCM (17)
Error: fmt_ subchunk size != 16. Is format code PCM?
WARNING: this file is not a valid WAVE file: siren-stereo-imaadpcm4.wav
xmlXPathCompiledEval: evaluation failed
runtime error: element apply-templates
Failed to evaluate the 'select' expression.
$

Test file could be downloaded from http://www.mediafire.com/?09db3whqa5z0kzq
(Run make imaadpcm4play-stereo.lib.swf inside the extracted folder)

The audio file in question is encoded as 44100 Hz 4-bit IMA-ADPCM Stereo.
The SWFmill Simple XML in question is written as follows:

<movie width="320" height="240" framerate="12">
    <background color="#ffffff"/>
    <frame>
        <library>
            <clip id="siren" import="siren-stereo-imaadpcm4.wav"/>
        </library>
    </frame>
</movie>

SWFmill: 0.3.3 (source)
System: Debian GNU/Linux 7.0 Wheezy i386