Mp3tag currently doesn't support editing the chapter information of M4B files (also often referred to as Nero tags).
With Mp3tag v2.83, you can remove the chapter marks by right-clicking on the file and selecting "Strip MP4 chapters". This will remove the Nero tags from the file and will allow you to edit the normal MP4 tag as usual.
I actually attached a sample file to the initial post, if you find that easier.
I have however noticed that mp3tag seems to be confusing mediainfo
Text [0/9997]
ID : 2
Format : Timed Text
Codec ID : text
Duration : 2 h 50 min
Bit rate mode : Variable
Bit rate : 0 b/s
Stream size : 116 Bytes (0%)
Language : English
Default : Yes
Forced : No
Alternate group : 3
Encoded date : UTC 1904-01-01 00:00:00
Tagged date : UTC 1904-01-01 00:00:00
Menus : 3
Menu #1
ID : 3
Codec ID : text
Duration : 2 h 24 min
Language : English
Encoded date : UTC 1904-01-01 00:00:00
Tagged date : UTC 1904-01-01 00:00:00
Bit rate mode : CBR
Menu For : 1,2
00:00:00.000 : 037
00:40:18.450 : 038
01:07:34.621 : 039
01:16:41.962 : 040
01:39:27.435 : 041
01:54:28.508 : 042
02:24:43.566 : 043
Menu #2
00:00:00.000 : M?ridien: A Silver Ships Novel, Book 3
00:40:18.450 : M?ridien: A Silver Ships Novel, Book 3
01:07:34.621 : M?ridien: A Silver Ships Novel, Book 3
01:16:41.962 : M?ridien: A Silver Ships Novel, Book 3
01:39:27.435 : M?ridien: A Silver Ships Novel, Book 3
01:54:28.508 : M?ridien: A Silver Ships Novel, Book 3
02:24:43.566 : M?ridien: A Silver Ships Novel, Book 3
When I look at the files on the binary level there is content being changed, it just doesn't to be parseable...
The track numbers are queried from the Nero chapter tags. I've analyzed your file and it has an additional text track which has again something that can be interpreted as track numbers (it's only numeric string data, this time with leading zeros starting at 001).
I'll focus on the Nero chapters for now, so yes – it's intentional.
I don't think that overloading the title, track, and pic make sense.
To be able to edit the chapter, it would make more sense to have a different view maybe?
Most(all I'm aware of) of the tools that work on these differentiate between them.
The chapter data is seen as additional meta data but doesn't prevent you working with the file level meta. As it is, although I can not edit the chapter meta, I can't seem to edit the meta that all players use who don'T support chapters.
Also I don't see how this would work with tag to filename renaming, it would rename the flle n times where n is the number of chapters.
I suppose you could add another entry for the file level tags, or have 2 modes, one that shows chapters and one that doesn't.
Also if I wanted to edit the chapter data, I'd probably also want to be able to edit the timestamps.