I created a Font style with large size and red color and set it on a Text annotation, it looks like no effective. But I added a spark line chart and set the Font style on title of spark chart, it looks like effective. Also I set string "',%,&,<,>" to title and TextAddOn and set isHTML of Font style to false, the title shows "',%,&,<,>", but TextAddOn just shows "',%,&,".
I think correct logic should be, if a Font style is set on Text annotation, it should overwrite the default styles of Text annotation.