USB Serial Device problem under Feisty

My company OEMs a USB serial based device. We have been able to use it with Ubuntu since the Breezy days with no problems.
(and every intermediate release). Under Feisty, when you power the device up, it starts up and immediately disconnects.
The exact same device works fine under Edgy and Dapper.

/var/log/kern.log

Jun 22 10:34:22 rice kernel: [856672.266982] usb 1-1: new full speed USB device using uhci_hcd and address 5
Jun 22 10:34:22 rice kernel: [856672.438876] usb 1-1: configuration #1 chosen from 1 choice
Jun 22 10:34:22 rice kernel: [856672.441818] ftdi_sio 1-1:1.0: FTDI USB Serial Device converter detected
Jun 22 10:34:22 rice kernel: [856672.441825] drivers/usb/serial/ftdi_sio.c: Detected FT8U232AM
Jun 22 10:34:22 rice kernel: [856672.442041] usb 1-1: FTDI USB Serial Device converter now attached to ttyUSB0
Jun 22 10:34:25 rice kernel: [856675.417958] usb 1-1: usbfs: interface 0 claimed by ftdi_sio while 'brltty' sets config #1
Jun 22 10:34:25 rice kernel: [856675.421344] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
Jun 22 10:34:25 rice kernel: [856675.421365] ftdi_sio 1-1:1.0: device disconnected

lsusb -c output (there were more devices connected but they are all working fine --- changing devices connected
   did NOT change behaviour)

Bus 001 Device 005: ID 0403:6001 Future Technology Devices International, Ltd 8-bit FIFO
Device Descriptor:
  bLength 18
  bDescriptorType 1
  bcdUSB 1.10
  bDeviceClass 0 (Defined at Interface level)
  bDeviceSubClass 0
  bDeviceProtocol 0
  bMaxPacketSize0 8
  idVendor 0x0403 Future Technology Devices International, Ltd
  idProduct 0x6001 8-bit FIFO
  bcdDevice 2.00
  iManufacturer 1
  iProduct 2
  iSerial 0
  bNumConfigurations 1
  Configuration Descriptor:
    bLength 9
    bDescriptorType 2
    wTotalLength 32
    bNumInterfaces 1
    bConfigurationValue 1
    iConfiguration 0
    bmAttributes 0xc0
      Self Powered
    MaxPower 90mA
    Interface Descriptor:
      bLength 9
      bDescriptorType 4
      bInterfaceNumber 0
      bAlternateSetting 0
      bNumEndpoints 2
      bInterfaceClass 255 Vendor Specific Class
      bInterfaceSubClass 255 Vendor Specific Subclass
      bInterfaceProtocol 255 Vendor Specific Protocol
      iInterface 2
      Endpoint Descriptor:
        bLength 7
        bDescriptorType 5
        bEndpointAddress 0x81 EP 1 IN
        bmAttributes 2
          Transfer Type Bulk
          Synch Type None
          Usage Type Data
        wMaxPacketSize 0x0040 1x 64 bytes
        bInterval 0
      Endpoint Descriptor:
        bLength 7
        bDescriptorType 5
        bEndpointAddress 0x02 EP 2 OUT
        bmAttributes 2
          Transfer Type Bulk
          Synch Type None
          Usage Type Data
        wMaxPacketSize 0x0040 1x 64 bytes
        bInterval 0
cannot read device status, Operation not permitted (1)

uname -a output

Linux rice 2.6.20-16-generic #2 SMP Thu Jun 7 20:19:32 UTC 2007 i686 GNU/Linux

for completeness dmesg output
[856672.266982] usb 1-1: new full speed USB device using uhci_hcd and address 5
[856672.438876] usb 1-1: configuration #1 chosen from 1 choice
[856672.441818] ftdi_sio 1-1:1.0: FTDI USB Serial Device converter detected
[856672.441825] drivers/usb/serial/ftdi_sio.c: Detected FT8U232AM
[856672.442041] usb 1-1: FTDI USB Serial Device converter now attached to ttyUSB0
[856675.417958] usb 1-1: usbfs: interface 0 claimed by ftdi_sio while 'brltty' sets config #1
[856675.421344] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
[856675.421365] ftdi_sio 1-1:1.0: device disconnected