DIvision by zero error when resizing disks

When resizing a VM disk on srv1, I get the following error:

Updating virtual disk on /kvm/joe3.cloud.virtualmin.com.img ....................... .. update failed : (mkdir -p \/tmp\/.webmin\/123349_13154_3_save_disk.cgi && mount -t xfs /dev/loop1 /tmp/.webmin/123349_13154_3_save_disk.cgi && xfs_growfs -D 2664448 \/tmp\/.webmin\/123349_13154_3_save_disk.cgi ; ex=$? ; umount /tmp/.webmin/123349_13154_3_save_disk.cgi ; rmdir /tmp/.webmin/123349_13154_3_save_disk.cgi ; exit $ex) failed : sh: ((: mkdir -p /tmp/.webmin/123349_13154_3_save_disk.cgi && mount -t xfs /dev/loop1 /tmp/.webmin/123349_13154_3_save_disk.cgi && xfs_growfs -D 2664448 /tmp/.webmin/123349_13154_3_save_disk.cgi ; ex=0 ; umount /tmp/.webmin/123349_13154_3_save_disk.cgi ; rmdir /tmp/.webmin/123349_13154_3_save_disk.cgi ; exit : division by 0 (error token is "/.webmin/123349_13154_3_save_disk.cgi && mount -t xfs /dev/loop1 /tmp/.webmin/123349_13154_3_save_disk.cgi && xfs_growfs -D 2664448 /tmp/.webmin/123349_13154_3_save_disk.cgi ; ex=0 ; umount /tmp/.webmin/123349_13154_3_save_disk.cgi ; rmdir /tmp/.webmin/123349_13154_3_save_disk.cgi ; exit ")

In all that mess, the actual error seems to be "division by 0", though I don't see where division is taking place. $ex has a 0 in it, but I don't see anything dividing by the exit value, so I dunno where the error is coming from.