Traditionally, when replying to text mails (I don't use HTML, so I don't know how it worked/works for this format), I could edit quoted text and press enter in the middle of a line, and kMail would split the line, prepending the newly created line with the quotation character and a space.

This made manually reflowing quoted lines pretty easy.

Since about KDE 4.11 (I think), this feature is broken:

Now splitting a quoted line using Enter will NOT insert a quotation mark and space character at the start of the newly created line, requiring several additional keystrokes for each line edited this way.

Reproducible: Always

Steps to Reproduce:
1. Reply to a (text?) mail
2. Position the cursor in the middle of a quoted line.
3. Press "Enter".
Actual Results:  
The line will be split and a new line without a quotation character prefix will be created.

Expected Results:  
A new line prefixed with the default quotation character will be created.