The reason this happens:
1) The code to add the Font Resource from file is incorrectly placed in a block that is only called when removing a previously loaded font: see BitmapDC::setFont in platform/win32/CCImage.cpp:160
font-face to load in the call CreateFontIndirectA is generated from the file name (taking the file name without the extension) however TTF files contain the font-face name in the definition. That means that if the font-face is not the same as the file name the operation will fail.
An example it the
Marker Felt.ttf provided as an example. The font-face in the TTf file is Felt so it will not load correctly without renaming.
1) Windows errors are not reported. For instance if AddFontResource fails to load the ttf file the error is not reported anywhere
2) The windows documentation says that the WM_FONTCHANGE should be sent with HWND_BROADCAST to inform all windows of the new font however the SendMessage is called with to a single specific window
3) The current design has additional Fonts generated for every Label instead of loaded once to the application and then reused.