The files are a bit large, but I'll see if I can cut one of them while keeping the CC track. Anyway, here's a bit more info on the CC track:
ID : 4-CC1
Format : EIA-608
Codec ID : c608
Duration : 1h 5mn
Source duration : 1h 5mn
Bit rate mode : Constant
Stream size : 0.00 Byte (0%)
Source stream size : 63.1 KiB (0%)
The MP4 file was made from a recording I captured from digital TV. I'd imagine this is fairly common.
The open source tool
CCExtractor is able to extract the captions and output them in SRT format. If you'd like to support the format, you may want to take a look. They encourage use of the code in other tools.