Sorry Timothy but i don't think we can call it a bug.
In a field definition, you specify the type of the field. When calculated, the result is automatically returned in this type.
But Data Viewer is not a field. If you specify in the formula multiple type argument, FileMaker cannot guess what type you wish get.
Thus the GetAs… functions are needed.
Yes, I just realized you can't expect FileMaker to interpret a date formatted as text (which is what GetValue gives you) correctly.