Changing text size in GtkTextView, using GtkTextTag scale property

[Cactus <medved_cool mail ru>]

Hello.
I have several objects GtkTextTag with different "size" property.
And there is another object GtkTextTag, which applies to all the text in 
GtkTextBuffer. Call it default_tag
I'm trying to change the scale properties of an default_tag object so 
that all the text in proportion to the size changed.
But the line is cut and creeps on each other. Screenshot: 
http://imgur.com/jZeiBMJ
I found idiotic solution. I change the window size by one pixel and the 
text is redrawn.
Is there a more normal solution?

P.S.:    gtk_widget_queue_draw - not working;
           tag-changed signal - not working