Comment # 6 on bug 1151174 from Johannes Meixner

I am not at all a udev expert so I may misunderstand things
related to udev or what udev might be able to do
if all was set up perfectly right.

According to my "udev end-user" experience things are even worse
because udev-configure-printer is not the only thing that could
get in the way while firmware upload needs to be the only thing
that should be allowed to happen.

For example also any pending print job gets in the way
when such a decice appears at the USB, cf.
https://bugs.launchpad.net/hplip/+bug/187049/comments/3
(excerpt):
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Of course another mess could happen if there are
pending jobs in the queue and CUPS starts to
send them (with exclusive device access) before
udev would try to upload the firmware.
-------------------------------------------------------------------

As far as I understand it the actual root cause is that
those devices show up at the USB as regular USB printers
(i.e. with the normal printer USB device class)
but as long as those devices do not have firmware
they do not behave as regular USB printers
(all they can do without firmware is receiving firmware and
 if they receive something else they basically "hang up").

But because they appear as a regular USB printers even without firmware
they are "just used" as regular USB printers by all normal software
which fails in arbitrary weird ways as long as those devices
do not have firmware that makes them regular USB printers.

Also any other (desktop) application that might query USB printers
could fail in arbitrary weird ways as long as those devices do not
have their firmware that makes them behave as regular USB printers.