I cannot reproduce what you see. I've done the following:

emacs -Q Options -> Customize Emacs -> Browse Customization Groups -> Emacs -> Editing -> Editing Basics -> Tab Width Replace the 8 with a 2 Click on `State` -> Set for Current Session 

then I went back to *scratch* and typed

x C-q TAB xx 

at which point I saw

xTxx 

rather than the

xT++xx 

[ where T and x both stand for whitespace. ]

I cannot reproduce what you see. I've done the following:

emacs -Q Options -> Customize Emacs -> Browse Customization Groups -> Emacs -> Editing -> Editing Basics -> Tab Width Replace the 8 with a 2 Click on `State` -> Set for Current Session 

then I went back to *scratch* and typed

x C-q TAB xx 

at which point I saw

xTxx 

rather than the

xT++xx 

[ where T and + both stand for whitespace. ]