  Let $\overline\F\_p$ be the algebraic closure of the prime field of
characteristic $p$. After observing that the principal block $B$ of
$\overline\F\_pPSU(3,p^r)$ is stably equivalent of Morita type to its Brauer
correspondent $b$, we show however that the centre of $B$ is not isomorphic as
an algebra to the centre of $b$ in the cases $p^r\in\{3,4,5,8\}$. As a
consequence, the algebra $B\otimes\_{\overline{\F}\_p}\overline \F\_p[X]/X^p$
is not stably equivalent of Morita type to
$b\otimes\_{\overline\F\_p}\overline\F\_p[X]/X^p$ in these cases. This yields a
negative answer to a question of Rickard.
