I do not know what ** is never used it my self but if it is a power sign then yes it is a bug. -2 is a number not a subtraction sign. Any mathematician can verify this. It is one of the "rules" of mathematics.
The usual rules of mathematics that I learned at school say that the expression -2^2 means: the number to be squared is 2, and the result is negated, i.e. we calculate -(2^2) = -4. That's what FPC does.
Excel and the usual formula parsers have a different convention, they put an invisible bracket around -2 and calculate (-2)^2 = 4 (like you do).
From what I learned at school I would say the Excel has a bug, but there are also arguments from the parser point of view for the opposite - that's what I was trying to explain above.
There's no chance to alter neither fpc nor Excel, that would break numerous calculations all over the world.
Again: that entire discussion would be avoided if people would use parenthesis in such unclear cases.
Aaah, I forgot: the ** operator is the same as the ^ in this discussion.