Font changes during the runtime in WPF app

I'm using a non English (Hebrew) font i开发者_开发技巧n a WPF application. The font was embedded in the project by expression blend.

In the designer I see the font correctly, but during the run time part of the letters are being changed to different font style.

What could it be?

---

Are the design and runtime environment on the same machine ? If not, check for installed fonts. If it's on the same machine, then maybe check if some localization happens on during runtime.