Regenerating Assemblies

So you open an assembly that you know needs to be regenerated (in my
case because I have a master part that I have modified which is
referenced into about 20 child parts). How do you stop the assembly
from regenerating? Ever since I have used ProE that "stop" button
comes up and you are supposed to be able to stop regen by clicking on
it. And ever since I have used ProE all it does is say, "Do you really
want to abort regeneration?" You click on "yes" and it ignores you and
continues regenerating.