Recently I installed Matlab 2013b on my laptop with windows 8.1 operating system. Whenever I open matlab, the fonts look normal, I think it uses lower resolution. As soon as I open MuPAD app or Simulink, the matlab window size suddenly changes and it starts on higher resolution and the font size is reduced. Same thing happens even if I use external monitor. I've attached two pictures, matlab screen shot before I open the app and matlab screen after I open the app. Compare the toolbar strips or command history font size and you can see the difference. The later is so small, that its hard to read on my desktop. I have intel HD graphics, that comes with i7 processor, as well as NVIDIA graphics processor.
Earlier I was using Matlab 2012a, and it never had this issue even on Windows 8.1, and same laptop.
Before opening MuPAD app or Simulink:
after opening MuPAD app or Simulink: