When you are setting row value with a button, the parenthesis are ignored in calculating the value.
This means that if you want to set the value to (5-1)/4 the result will be 4.75 and not 1 as it should be.
Obviously, this isn’t a problem when using static numbers, but the same happens when you replace those numbers with other formulas.
This is a very serious issue which should be fixed as soon as possible.
If I were to guess, I would say this is because button actions are converted into “parse later” and during that conversion the parenthesis are being skipped.
Workaround
Transforming your equations into their expanded form (so the formula would be 5/4-1/4) should fix the issue. You can even use wolfram alpha for complex formulas.
Another, slightly better workaround would be to replace all () with Sum().
And here is a proof that this bug is actually real: