Alpha level of ForegroundRole ignored during repaint if FontRole returns bitmap font

For some items of my QAbstractTableModel subclass, I return a ForegroundRole with a 50% alpha level. This works for all columns except the one I also return a FontRole - with that column, the alpha level of ForegroundRole is used initially, but lost on repainting (usually almost immediately).

Update: This seems to only apply when the font in question is a bitmap font