Why do the errors in a formula depend on how it's written?

Let there be an equation, let's say $V=IR$. Now when we write its error formula we write it as

$$\frac{\Delta V}{V} = \frac{\Delta I}{I} + \frac{\Delta R}{R}.$$ Now let us take example values. For instance let $V=12$, $I=3$, $R=4$, and $\Delta I=3\%$ and $\Delta R=2\%$. Hence the error in $V$ is $\Delta V=18\%$.

Now we can write Ohm's law as $I=\frac{V}{R}$. Now we get the error in $I$ to be

$$\frac{\Delta I}{I} = \frac{\Delta V}{V} + \frac{\Delta R}{R}.$$ Keeping the same values of $\Delta V=18\%$ and $\Delta R=2\%$, we get $\Delta I=6\%$. Why is this different? According to the formulas for $\Delta V$ and $\Delta I$, in both cases we will surely get the different values, but why is it that we get different error values for the same pair of values of R,V and I?