IPhoto treats two identical video cameras in totally different ways

I own two Canon Vixia HF G20 video cameras. The two cameras are, as far as I can tell, configured in completely identical ways. And yet for some reason when I connect them to my Mac to import video, completely different things happen:

• When I connect one of the cameras, iPhoto launches automatically, the camera appears under "Devices" in the iPhoto sidebar, and I have the option to import video directly into my iPhoto library.
• When I connect the other camera, iPhoto does not launch automatically. If I launch it manually, the camera does not appear under "Devices", and there does not seem to be any way to get iPhoto to recognize that the camera is connected, or to import video from it. Instead I have to navigate to the AVCHD file in the Finder, open video clips using Quicktime Player, and then use Quicktime Player to Save the clips to my hard drive. (This method works on the other camera, too, of course.)

Since I am able to save video from both cameras to my HD, this difference in behavior is not mission-critical, but it is annoying and mysterious. I am not sure if the difference has to do with a setting in iPhoto, or on the camera itself, or what. Can anybody explain to me why these two cameras — same model, same configuration (AFAIK) — are handled by the OS so differently?

Edited to add:
User tubedogg asked:

When it's connected, go to Apple menu > About > System Report button. What does the USB bus report for the port where it is plugged in?

So here is what shows up for Camera 1 (the one that is recognized by iPhoto and Image Capture):

    Video Camera:

  Product ID:   0x326e
  Vendor ID:    0x04a9  (Canon Inc.)
  Version:  0.01
  Serial Number:    [redacted]
  Speed:    Up to 480 Mb/sec
  Manufacturer: CANON Inc.
  Location ID:  0x1d110000 / 7
  Current Available (mA):   500
  Current Required (mA):    100
  Capacity: 31.44 GB (31,439,454,208 bytes)
  Removable Media:  Yes
  Detachable Drive: Yes
  BSD Name: disk4
  Partition Map Type:   MBR (Master Boot Record)
  S.M.A.R.T. status:    Not Supported
  Volumes:
CANON:
  Capacity: 31.44 GB (31,435,259,904 bytes)
  Available:    31.42 GB (31,421,562,880 bytes)
  Writable: No
  File System:  MS-DOS FAT32
  BSD Name: disk4s1
  Mount Point:  /Volumes/CANON
  Content:  Windows_FAT_32
  Volume UUID:  31F58768-8479-3FC8-8CA0-405944EBAC64

and here is what shows up for Camera 2 (the one that is not recognized by iPhoto or Image Capture):

Video Camera:

  Product ID:   0x326e
  Vendor ID:    0x04a9  (Canon Inc.)
  Version:  0.01
  Serial Number:    [redacted]
  Speed:    Up to 480 Mb/sec
  Manufacturer: CANON Inc.
  Location ID:  0x1a120000 / 4
  Current Available (mA):   500
  Current Required (mA):    100
  Capacity: 31.44 GB (31,439,454,208 bytes)
  Removable Media:  Yes
  Detachable Drive: Yes
  BSD Name: disk4
  Partition Map Type:   MBR (Master Boot Record)
  S.M.A.R.T. status:    Not Supported
  Volumes:
CANON:
  Capacity: 31.44 GB (31,435,259,904 bytes)
  Available:    31.42 GB (31,423,430,656 bytes)
  Writable: No
  File System:  MS-DOS FAT32
  BSD Name: disk4s1
  Mount Point:  /Volumes/CANON
  Content:  Windows_FAT_32
  Volume UUID:  F1025F17-85DA-3580-845F-054D9A32D2A6

As you can see, the results are pretty much identical.

Edited again: Mystery solved! I will post it as an answer below, for the benefit of anybody who ever has this (or a similar) problem.