removing certain umass (cd/dvd?) devices appears to lock up the USB bus on 14.2/14.3 (at least)

I have a USB DVD drive that when I unplug (even when empty and 
unmounted) appears to stop the entire USB stack on 14.2/14.3. There are 
no errors (that I can see) in the dmesg, it *appears* to detach, but 
then no other USB events happen.


I originally thought it was just the port that it was attached to, but 
in recent experimentation I attached it to a USB hub, then detached it 
from the hub, and even other ports on the host stopped responding.  
Currently connected devices appear to continue to work, but if removed 
nothing will reattach to those ports.


This has now happened across a couple of different machines with this 
device, so I don't think it is host specific behavior


When trying to run 'usbconfig -v - l' to get some kind of diagnostics it 
just hangs; C-t yields the following:


 > load: 0.12  cmd: usbconfig 52496 [USB config SX lock] 3.12r 0.00u 
0.00s 0% 2280k


Of course in the interests of a fresh reproduction for this email, it 
just worked; I am continuing to attempt to reproduce. Suggestions of 
things I should try when I am successful to diagnose the issue so we can 
fix it?

The relevant USB attach messages are:

ugen1.10: <Hitachi-LG Data Storage Inc Portable Super Multi Drive> at usbus1
umass0 on uhub4
umass0: <Hitachi-LG Data Storage Inc Portable Super Multi Drive, class 
0/0, rev 2.00/0.00, addr 14> on usbus1
umass0:  8070i (ATAPI) over Bulk-Only; quirks = 0x0000
umass0:1:0: Attached to scbus1
cd0 at umass-sim0 bus 0 scbus1 target 0 lun 0
cd0: <HL-DT-ST DVDRAM SP80NB80 RC00> Removable CD-ROM SCSI device
cd0: 40.000MB/s transfers
cd0: 0MB (1 0 byte sectors)
cd0: quirks=0x10<10_BYTE_ONLY>

Detach messages are:

ugen1.10: <Hitachi-LG Data Storage Inc Portable Super Multi Drive> at 
usbus1 (disconnected)
umass0: at uhub4, port 2, addr 14 (disconnected)
cd0 at umass-sim0 bus 0 scbus1 target 0 lun 0
cd0: <HL-DT-ST DVDRAM SP80NB80 RC00>  detached
(cd0:umass-sim0:0:0:0): Periph destroyed
umass0: detached