In this note, we construct a convolution lattice that is not only a sublattice of \((\textbf{m}^{\textbf{n}},\le _{\sqcup })\) but also isomorphic to the pentagon. As a result, \((\textbf{m}^{\textbf{n}},\le _{\sqcup })\) determined by \(\sqcup \) is not distributive for \(m,n\ge 3\) , which proves a conjecture related to the distributivity of convolution lattice. Furthermore, we verify that \((\textbf{2}^{\textbf{n}},\le _{\sqcup })\) is distributive for \(n\ge 2\) , and \((\textbf{m}^{\textbf{2}},\le _{\sqcup })\) is not distributive for \(m\ge 3\) .