  Let $\mathrm{pm}(G)$ denote the number of perfect matchings of a graph $G$,
and let $K_{r\times 2n/r}$ denote the complete $r$-partite graph where each
part has size $2n/r$. Johnson, Kayll, and Palmer conjectured that for any
perfect matching $M$ of $K_{r\times 2n/r}$, we have for $2n$ divisible by $r$
\[\frac{\mathrm{pm}(K_{r\times 2n/r}-M)}{\mathrm{pm}(K_{r\times 2n/r})}\sim
e^{-r/(2r-2)}.\] This conjecture can be viewed as a common generalization of
counting the number of derangements on $n$ letters, and of counting the number
of deranged matchings of $K_{2n}$. We prove this conjecture. In fact, we prove
the stronger result that if $R$ is a uniformly random perfect matching of
$K_{r\times 2n/r}$, then the number of edges that $R$ has in common with $M$
converges to a Poisson distribution with parameter $\frac{r}{2r-2}$.
