Hi. I'm not sure if that error is a bug or a feature. Because it prevent an unusual task: using degrees scale temperature (those that have an offset) in a multiplication, where the usual is using the "new" Delta scale temperatures. I take my time to understand why it's neccesary to use Delta's, but get convinced after some good Martin's explanations (here).
I agree with Alvaro. The result is actually correct. I do believe it's still a bug, however, as you can add/subtract degC with seemingly strange, but correct, results.
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