RTTI not Working

I'm using CW IDE 5.8 Build 1919 to build Adobe PlugIns on MacOS X 10.4.4
...but I'm finding that the RTTI calls:
dynamic_cast<MyClass*>(myObjectPtr) always return nil
and typeid(*myObjectPtr)    and    typeid(*myObjectPtr).name()
return junk.

I have turned the RTTI setting on and tried #pragma RTTI on;
The same code worked using MW IDE for Windows

Has anyone run into a similar problem?

Thanks for your time.
Pete