FreeBSD 7.0 Mount Strangeness

[dfeustel at mindspring.com]

I have encountere what seems to be strangeness in the way mount works
when mounting msdos file systems on usb mass storage devices.  I have a
14-in-one usb reader connected to my computer running AMD 64-bit FreeBSD
7.0 release. At boot, there are four special files in /dev for the usb
devices: /dev/da[0-3]. All attempts to mount an msdos file system using
the command "mount -t msdosfs /dev/daNs1 /mnt" fail with the message "no
such file or directory". Checking /dev, there are no special files of
the form daNs1. If I then do "mount -t msdosfs /dev/daN" I get the
message "invalid argument", BUT there is now in the /dev directory an
entry daNs1, and the next "mount -t /dev/daNs1 /mnt" command succeeds
:-).  This behavior is repeated for each mount of an msdos file system
on a previously unused device socket on the usb reader. The newly
created devices remain after they are unmounted, so this problem goes
away until reboot, at which time the device files of form daNs1 are
deleted. 

I have not found any FreeBSD documentation of this behavior yet. 
Is this behavior known and expected? (I'm a FreeBSD newbie.)

Thanks,
Dave Feustel