Custom "spell-check" sometimes not working?

This is a weird problem, I write a lot of different languages on my computer, and since my keyboard doesn't have all the keys in the world, I have made certain key-combinations that replaces them with another letter.

For example, "†˛" becomes "þ" and "∂∂" becomes "ð". Now that works fine, but I also have added "œœ" that is supposed to become "ǫ", but form some reason that special "spell-check" does not work while the others do.

Is there any reason for this? I'm using the Yosemite 10.10.2, the same problem exists on the 10.0.3 DP.