I have a strange problem with a USB flash drive. After a fresh reboot,
the device of the drive's partition (/dev/sda1) does not exist:

[~]$ mount /mnt/flash/
mount: special device /dev/sda1 does not exist


The only way I've found to make it show up is to attempt to mount the
device itself as root:

>>>ROOT<<< [~]# mount /dev/sda /mnt/flash
mount: you must specify the filesystem type


This fails for obvious reasons, but immediately after running this
command, the "real" device /dev/sda1 shows up, and works fine as a
normal user. The above command only has this effect when run as root;
a normal user can't make this happen. Here's the relevant fstab entry:

/dev/sda1 /mnt/flash vfat
noauto,sync,users,umask=000,defaults 0 0

Does anyone know what's going on? Is there something I can do to make
the device properly available on boot? After doing the workaround
above, the device works perfectly well and can be mounted and unmounted
by a normal user, until the next reboot.