This is not a duplicate of MC-1572 as the "bug" is the opposite of that report.

Formatting codes using the section symbol should not be possible from within the game (see comments on MC-1572). This is however possible using a keyboard that supports that character, such as a Norwegian layout.

This bug appears to affect the UI of signs, and the UI of book and quills, but no other places where text can be inserted.

Expected Result:

Book with black text and no formatting as the formatting is not supposed to be supported from within the game

Observed result:

Formatted text, see attached screenshot

Steps to reproduce this:

1. Set your keyboard to a Language that can type the section sign (§) without alt-code, such as Norwegian.
2. Type only that character in a raw-text-application such as notepad with the key Shift+| (the key left of 1 on the norwegian keyboard layout). type that character, and copy it.
3. Open Minecraft and edit a book & quill paste the symbol § with Ctrl+v, then immediatly followed by typing a single character from the format codes (0-9,a-f,k-o) 
4. This will appear as invisible, but the next character(s) typed will however have the formatting applied

Important side information:

The section symbol must be copied by itself, as any combination of characters will not work even if they are the correct combination to add formatting