Hibernate breaks when booting with USB device attached (/dev/sda* changes to /dev/sdb*)

Is the PC's BIOS set to try starting from USB before hard-disk?

If so, and there's a USB device plugged in when the system resumes from hibernate, the BIOS may have re-ordered the devices making the USB device first. This would explain your symptoms.

If the BIOS is set this way, try moving the USB device to a position after the hard-disk in the boot order.

Not sure about that, but I don't think this laptop even supports booting from USB ... I'll check it out. I was, however, thinking that it may be a BIOS thing - would it be possible that having USB legacy support enabled in BIOS is contributing to this problem?

What you've described is a re-ordering of the detected drives *only* when the USB device is connected. This is what a PC BIOS does when it scans the boot-device list.

If the printer or other connected USB device has a storage-card adapter it may cause the PC BIOS to detect a drive. If the USB devices don't have storage-card capabilities it could be the PC BIOS has a bug and is mis-detecting. It is worth upgrading the PC BIOS if a newer one is available and won't break anything else.

Please give the PC make, model, and BIOS revision, and the model # of the device(s) attached when this happens.

Yes, the USB printer that is attached when causing this problem is a HP Photosmart 2710, which has a storage-card adapter. What you say makes sense, as the problem doesn't occur with a USB wireless adapter - so I'm guessing that the BIOS must be set to boot from USB before local disks. Unfortunately, i won't be able to have a look at the clients machine for a few days to confirm.

The laptop is a Pioneer M3 (?) ... I wasn't able to find much on it, but it's possibly a very similar machine to the Toshiba M3.

Pages 5-12 & 5-13 of the Pioneer M3xxS manual cover the BIOS Boot menu:

"When you turn the computer on it will look for an operating system (e.g. WindowsXP) from the devices listed in this menu, and in this priority order. If it cannot find the operating system on that device, it will try to load it from the next device in the order specified in the Boot Menu."

"If you wish to boot from a CD-ROM you will need to add it to the boot order.
As a general rule the order below is recommended:
1. Removable Devices (usually floppy disks)
2. CD-ROM/DVD-ROM Drive
3. Hard Drive
4. Network Boot
In everyday use you will usually boot from the hard drive, however there may
be occasions when it is advantageous to boot from a floppy disk or CD-ROM/
DVD-ROM."

In their jargon I suspect "Removable Devices" isn't limited to floppy disks, but includes USB devices as well.

I'm going to be finalizing this issue for a client today ... just wondering, though - where did you find the BIOS manual for this machine? have you got a link?