I don't know exactly how, but I managed to make it work. I had to click multiple times in the button to show/change font size for the selected text and then to also change the measure (pt, px, cm, mm...) and then hammering down (trying new numeric values for spacing between lines) and pressing enter occasioanlly worked.
It showed me, however, two values. As soon as I clicked the font size of the selected size the number changes for another one. And upon a new mouse click it got back to the original (previous number). Any ideas?