Hmm ... weird indeed. Wouldn't you by chance have two entries for hda3 in fstab, say one for /usr and another for /mnt/hda3, or something?
I did a Knoppix 3.4 HD install to a Compaq 433 Mhz box. I partitioned the disk like this:
/dev/hda2 to / (about 2.5 GB)
/dev/hda3 to /usr (about 18 GB)
I selected the ext2 filesystem type. Everything works pretty well, except that when I shut down I have been noticing a message like "/dev/hda3 not mounted". This is *not* true--it is mounted, is listed in /etc/fstab and also in /etc/mtab (and of course the system would not operate without access to /usr). Later, when I start it up, another message says "/dev/hda3 not cleanly unmounted, forcing filesystem check". The check takes a couple of extra minutes during bootup. This happens at *every* boot. Of course, the check completes with no problems reported, and the boot sequence continues. Once booted, everything's functionally OK.
I've checked the boot scripts for mount and umount commands and it all seems in order.
I used a non-Knoppix rescue disk to boot up, then mounted and manually checked both /dev/hda2 and /dev/hda3. Using the ext2 filesystem utilities, I discover that /dev/hda3 is, for some reason, marked "dirty" at first, but I can clean it up, restart Knoppix, and it mounts right up with no problems. I shutdown and restart Knoppix, and /dev/hda3 is dirty again--another check forced.
I'm beginning to think that either Knoppix or Debian are somehow bypassing /etc/fstab and the boot scripts.
The only other odd behavior I can see is that a "shutdown -h now" command seems to power off the system before the shutdown scripts finish...
Hmm ... weird indeed. Wouldn't you by chance have two entries for hda3 in fstab, say one for /usr and another for /mnt/hda3, or something?

Intel Core i7-3770K 3.5 GHz Processor
$39.00
Intel Core i7-9700 3.0 GHz Octo-Core (SRG13) Processor
$79.00
INTEL CORE I9-10940X X-SERIES PROCESSOR | 3.30GHZ | SRGSH
$179.99
BOSGAME E4 Air Mini PC, AMD Ryzen 5 3500U 8GB DDR4 256GB SATA SSD
$169.99
Intel Xeon E3-1230 v3 SR153 3.3GHz Quad Core LGA 1150 CPU Processor
$14.49
Intel Core i7-9700 SRG13 3.0 GHz Desktop CPU
$80.00
(USED) AMD Ryzen 7 7800X3D 100-100000910WOF AM5 CPU Processor Box Not Included
$259.99
Intel Core i5-7500 SR335 3.4GHz 4-Core LGA 1151 CPU PROCESSOR
$14.99
AMD Ryzen 7 PRO 8700GE 8-Core/16-Thread Up to 5.1GHz AM5 (FL1)
$189.00
Intel 6th Gen Core i7-6700K 4.0GHz (Turbo 4.2GHz) 4-Core LGA1151 CPU SR2L0
$38.00