Yeah, that seems just unclear language and because it's trained on human language, 'is' does not equal 'equals'. Using 'equals' will help.
Even before computers we created formal languages (mathematics, logic equations) precisely because human language is too often ambiguous.
Yes, and fitting just those cases would result in a model that handled other cases incorrectly, because idioms inconsistent with that rule exist. (“Jodie is the bomb” has a meaning distinct from the individual words taken separately which is not stating a reflexive equivalency, for instance.)