File fieldtype in a repeater

I'm running Perch 2.8.18 and I've set up a repeater, like so:

<perch:repeater id="performance_music" label="Music" divider-before="Performance Music" order="3">
        <perch:if exists="performance_music_file">
        <hr>
        <perch:content id="performance_music_title" type="text" size="xl" textile="false" label="Song Title" required="true" /><perch:if exists="performance_music_artist"> – <perch:content id="performance_music_artist" type="text" size="xl" textile="false" label="Artist" /></perch:if><br>
        <audio controls preload="none" autobuffer>
        <source src="<perch:content id="performance_music_file" type="file" bucket="performance-music" label="MP3 File" output="path" />" type="audio/mpeg" />
        Your browser does not support the <code>audio</code> element.</audio>
        </perch:if>
</perch:repeater>

The problem is when I select a file, it doesn't show that a file has been selected (although it has sometimes but after clicking save, it disappears again from the selection). I've tried it with MP3 and PDF files.

Any idea what's going on? Can the file fieldtype not be used in a repeater?