HLS muxed audio missing format label

We have the following HLS (live) master playlist:

```
#EXTM3U
#EXT-X-VERSION:6
#EXT-X-INDEPENDENT-SEGMENTS
#EXT-X-STREAM-INF:BANDWIDTH=130780,CODECS="mp4a.40.2",AUDIO="aac-primary"
../..//chunklist_ao.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=130780,CODECS="mp4a.40.2",AUDIO="aac-backup"
../..//chunklist_ao.m3u8
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac-primary",NAME="Home",LANGUAGE="eng",DEFAULT=YES,AUTOSELECT=YES,CHANNELS="2"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac-backup",NAME="Home",LANGUAGE="eng",DEFAULT=YES,AUTOSELECT=YES,CHANNELS="2"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac-primary",NAME="Away",LANGUAGE="eng",URI="../..//chunklist_ao.m3u8",DEFAULT=NO,AUTOSELECT=YES,CHANNELS="2"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac-backup",NAME="Away",LANGUAGE="eng",URI="../..//chunklist_ao.m3u8",DEFAULT=NO,AUTOSELECT=YES,CHANNELS="2"
```

Based on the `HlsPlaylistParser` (line 514), if an audio track has no URI defined, then it will be stored in the `muxedAudioFormat`. However in this case, whenever we query the audio tracks, the muxed one has no id/label in the `Format`.

See the event logger's output:

```
MediaCodecAudioRenderer [
Group:0, adaptive_supported=YES_NOT_SEAMLESS [
[ ] Track:0, id=0, mimeType=audio/mp4a-latm, bitrate=130909, codecs=mp4a.40.2, channels=2, sample_rate=48000, supported=YES
[ ] Track:1, id=1, mimeType=audio/mp4a-latm, bitrate=130909, codecs=mp4a.40.2, channels=2, sample_rate=48000, supported=YES
]
Group:1, adaptive_supported=YES_NOT_SEAMLESS [
[X] Track:0, id=aac-primary:Away, mimeType=audio/mp4a-latm, codecs=mp4a.40.2, channels=2, sample_rate=48000, language=en, label=Away, supported=YES
[ ] Track:1, id=aac-backup:Away, mimeType=audio/mp4a-latm, codecs=mp4a.40.2, channels=2, sample_rate=48000, language=en, label=Away, supported=YES
]
```

This is causing a problem for us, as we would need to select the tracks based on the labels. The question is whether the missing labels of muxed audio tracks is intentional or if it's a bug? How could we workaround this issue on our side (without changing the manifest itself)?

Thanks in advance.