QGIS » QGIS Application

Hello,

I am trying to label my polygons using Single Label option.

I have set labeling to be in relation to the string from Attribute table column called "Simboli"
That column contains a set of different labels that were written using HTML sub and sup codes (e.g. "K₂^2,3"). (see Fig. number 1)
After that, If I choose Expression dialogue, under the "Output preview" I can see regular formatted Label, as I wanted it to be. (see Fig. number 2)
But, when I save everything, close all windows and come back to the map, again I can see only codes on my map (see Fig. number 3), instead properly sub and sup formatted numbers (or letters etc.)

I suppose that this the bug, since within the "Output" preview everything is fine, but not on map canvas.
Or maybe I didn't set something properly? I need this kind of labels in map canvas, not on print composer for which I know that support HTML rendering.