text-scale-decrease changes text-scale-mode without font changes

[fatiparty]

I am using these two keybindings for chanding the font in emacs.  But I am 
getting text-scale-mode with a integer number decreasing (-1,-2,-3,...) when 
using "C-,".  Whilst for  "C-.", the integral number increasing.

Still the text height in the emacs buffer is not changing.

(global-set-key (kbd "C-,") 'text-scale-decrease)
(global-set-key (kbd "C-.") 'text-scale-increase)