Why do I disagree with my calculator? I followed the order of opperations but my answer disagrees with my calulator's.

Problem: $331.91 - 1.03 - 19.90 + 150.00$
Calculator answer: $460.98$
My answer: $162.98$

Why the discrepancy?

It is clear that you did the operation $$331.91 - 1.03 - (19.90 + 150.00) $$ while the calculator instead simply did $$(331.91 - 1.03 - 19.90) + 150.00$$
A strict order of operations (PEMDAS) is in some cases not really the actual convention used in actual mathematics in some sense. When you see something like 
$$3.2345-9000+2345$$ the intent of the author is 
$$(3.2345-9000)+2345$$ as subtraction is really just addition by a negative (as division is just multiplacation by an inverse) and it is quite convenient to just work left to right in these cases.
