The pages tag is inconsistent between written books and writable books

Let's start!

Use command:

1. /give @p writable_book{pages:['[{"text":"123"}]']}

2. /give @p written_book{pages:['[{"text":"123"}]'],title:CustomBook,author:Player}

then get: (book content)

1. [{"text":"123"}]

2. 123

get a wrong? so I try to get their NBT:

1. pages:['[{"text":"123"}]']

2.pages:['{"text":"123"}']

and I try a command:

/give @p writable_book{pages:['[{"text":"123"}]'],title:CustomBook,author:Player}

but I get

123

the "pages" NBT is the same, but I get a different result?

 (Can't use the list in the writable book?