Build 5355-60: demuxed MP4 files not playable

[meRobs]

Because of a post (viewtopic.php?f=17&t=12486) by liyangmediacoder, I tried demuxing a VOB, MKV and an MP4 file in build 5355.
First, I tried with settings to suit a WMV file, according to the Encoding Guide (viewtopic.php?f=17&t=9643) and simply changed Task Mode to "Demux".
All tabs remained as before (suits WMV ie ASF) except that the Demux tab had Demux Audio and Demux Video checked with MPlayer as the demuxer and the Extension were set blank.

The VOB source gave valid MPV video and AC3 audio files and both played in VLC

The MKV source gave a video with no extension and an MPA audio file (correct extension). Both had valid sizes with useful content (MediaInfo) and played in VLC, after the video extension was changed to M4V.

However, the MP4 source file gave a video with the "264" extension and an AAC file. Neither displayed useful content, according to MediaInfo. On the other hand, the file sizes were correct, so they contained the data but their headers were ~empty!. Of course, changing the extension of the video file made no difference.

[meRobs]

I just examined the later build 5358 and it gave a playable video file (M4V) but an AAC file that had its data but was not playable because of an incomplete header. This seems a little different from 5355, though, because I used a different MP4 source file!?
In all cases, the AAC audio files demuxed from the MP4 source files had incomplete headers.
The result in build 5175 was similar.

By contrast, VOB and MKV source files demuxed correctly.

[meRobs]

I have just tried the x64 version of build 5360.
I used both
(1) Revert All Settings + Mode= Demux or
(2) the Preset for WMV (Encoding Guide) then Mode = Demux.

In both cases an MPEG2 source file demuxed to files with complete headers and they played in VLC.

However, two different MP4 source files demuxed to files of the ~correct size but their headers were ~ empty and they failed to play!