As per my understanding, the simple mathematical order of operations("Operations" mean things like add, subtract, multiply, divide, squaring, etc.), is
Exponents (ie Powers and Square Roots, etc.)
Multiplication andDivision (left-to-right)
Addition andSubtraction (left-to-right)
Divide and Multiply rank equally (and go left to right).
Add and Subtract rank equally (and go left to right)
Thus in your case for the Multiplication and Division the ranking is equal. That can be a reason the Parenthesis are being removed. If you try with some other operations Like Multiplication and Addition then the Parenthesis will not be removed.
Indeed Anaplan removes the un-necessary parenthesis when are used logical or mathematical operators that have the same priority.
I was surprised as well in the first place when I noticed this.
I think this has to do with the optimization of the Anaplan calculation engine in order to parallelize as much as possible.
When parenthesizes are present, the calculation engine is obliged to follow a particular order of the calculation... without them, Anaplan can calculate in parallel (so quicker) some parts of the formula and returning, in the end, the same result.