When searching a math problem, example being -3(16)+47, it will give the wrong answer, giving 34 instead of -1. This issue seems to only occur when using the parenthesis as a way of multiplication, but it is still annoying to have to use * to make the browser know that you want to multiply.
The thing is, this isn't even an issue for almost all calculators, as they all use parenthesis as multiplication, yet Opera doesn't for some reason.

Yes, that sounds annoying. Because Opera's search bar isn't a true calculator, it doesn't always interpret mathematical phrases in the same manner. Thus, unless you specifically use *, -3(16)+47 is not recognised as a multiplication. The safest fix at the moment is to add the *. A good calculator app or an online tool for math input is preferable if you want something that can handle brackets multiplication natively.