Let $K$ be an unknot in $8$-bridge position in the $3$-sphere. We give an example of a pair of weak reducing disks $D_1$ and $D_2$ for $K$ such that both disks obtained from $D_i$ ($i = 1, 2$) by a surgery along any outermost disk in $D_{ 3-i}$, cut off by an outermost arc of $D_i \cap D_{ 3-i}$ in $D_{ 3-i}$, are not weak reducing disks, i.e. the property of weak reducibility of compressing disks is not preserved by a disk surgery.
Categories: math.GT