Text cursor is positioned wrong when using tab key at tab stops

When using tab key at a tab stop position, the cursor is placed wrong.

1. Open a text file in Creator
2. Make sure Insert spaces instead of tabs in preferences is off. And the tab size is 4.
3. In a new line, type "1234" and notice the line and col position at the top-right of the window. It should say "Col: 5" and the cursor is right next to the letter "4."
4. Hit the Tab key.
5. Note that the Col position now say "Col: 9" but the cursor is still right next to the letter "4" instead of 4 character width away.

It's like there's a invisible/nun-functioning tab character added. All the column position int the line from that point on is wrong.