To reproduce:

1. Download attached project "896661.zip" and open it in Unity
2. Open "Title" scene
3. Select "Game" view
4. In Project window go to "fonts" folder
5. Select "Asset.ttf"
6. In a "Inspector" window set "Font Size" to "200"
7. Make sure that "Character" type is set to "Dynamic"
8. Hit "Apply" button

Expected result: After you pressed "Apply" button, in "Game" view you will see, that text resolution changed
Actual result: After you pressed "Apply" button, in "Game" view you will see, that text resolution doesn't changed

Note: If you select "Character" type to "Unicode", "Font Size" resizes text

Reproduced on Unity 5.5.3f1, 5.6.0f3 and 2017.1.0a6
Could not check for regression in 5.4.x, because files can not be loaded

Video is in "Font size is broken.zip" file