tab size modification doesn't work consistently

On autocomplete setting tab, if user changes the tab size to 8, then each time the tab should be displayed as 8 spaces.

Somehow it has strange behavior:
1. Copy and paste following queries in the editor;
2. edit the tab size and enable "show invisibles";
3. press one tab on first line; 2 tabs on 2nd line; and 1 tab on third line
4. Observe the UI (first line tab displays "5 dots"; 2nd line tabs display 1+8 dots; 3rd line tab display 3 dots.
Please see attached screenshot for details.

"
describe customers;
select * from customers where id=10326;
select 'Hello World';
"