>Some of you probably already knew this, but it caught me off guard...
>

Are you sure that's what's happening? Are you sure your base class always returns a number (and doesn't have some cases where it just does a RETURN out of the code)?

I tried it and it works fine:

o = CREATEOBJECT("TestB")
?o.DoSomething("")

DEFINE CLASS TestA AS Custom
   FUNCTION DoSomething(tcString)
      RETURN 1
   ENDFUNC
ENDDEFINE

DEFINE CLASS TestB AS TestA
   FUNCTION DoSomething(tcString)
      RETURN DODEFAULT(tcString)
   ENDFUNC
ENDDEFINE