unexpected EOF for some fmp4 files

[threadedstream]

I'm muxing mpeg-ts from fmp4, and for some fmp4 files mp4 demuxer returns unexpected EOF error.
It happens inside ReadPacket when calling

if _, err := io.ReadFull(demuxer.reader, sample); err != nil {
            return nil, err
}

I wonder if it's a normal behaviour for some fmp4 files or is there a bug in offset calculations?

P.S
I can't provide "faulty" fmp4 files for security reasons