- 
    
Bug
 - 
    Resolution: Fixed
 - 
    
P2: Important
 - 
    6.8.0
 - 
    None
 
- 
        91d93a739 (dev), 2c3ba45be (6.10)
 
The documentation of QTextFormat::FontSizeAdjustment says:

This does not explain what values it actually takes (int only), and how they are applied to the font size. It sounds a bit like it could be a float that gets multiplied with the base size.