Let $A$ be a set with at least three elements.
If $\mathcal P = \{B_1 ,B_2, B_3\} $ is a partition of $A$, is $\{B_1^c , B_2^c,B_3^c\}$ a partition of A?
So I am thinking the answer is no, since there is the possibility that two or more elements of $\mathcal P $ may be equal.
$A=\{1,2,3\}$. $\mathcal{P}=\{\{1\},\{2\},\{3\}\}$. Then $\{1\}^c = \{2,3\}$ and $\{2\}^c=\{1,3\}$, so $\{1\}^c\cap \{2\}^c = \{3\}\neq \emptyset$.