These anomalies arise as a result of the low light situations we shoot in.  Digital cameras are good at compensating for low-0 light conditions with a combined effort from the flash and it's control over aperture and shutter speed.  Add in the camera CCD's ability to see into the IR spectrum and digital cameras do pretty well at shooting in the dark.

They are not flawless however.  Digital CCDs still fall victim to many of the same constraints conventional film does.  Even though the process is different, the principals are still the same.   Low-light still presents the same pitfalls for digital photography that it does for film photography.

Light trails are not as common in digital due to the power of the flash combined with a software package designed to get enough light into the camera for a proper picture - but they do turn up.  A major culprit is the camera's settings, which take some level of control from the software depending on what they are set at.  For example, if your camera is set for action or sports the shutter speeds are bumped up to stop the action of fast moving subjects.  This will limit how slow the camera can drop the shutter speed.  Shooting in this mode in 0 light will net you dark photos.

In most cases, light trails are caused by a slow shutter speed combined with camera shake and a bright source of light (including a reflection).  Digital camera software is decent at interpreting what it sees - which allows the shake to be compensated for, but a bright source of light will still cause an overexposure with these slow shutter speeds.  Add in the shake and what you have are bright, seemingly erratic light trails in your pictures.  What you will find interesting about the following photos (and ultimately what causes many photos like this to be passed off as evidence) is the fact that the photos themselves are sharp, clear, in focus and have no signs of camera shake - aside for the trails.  YES it is possible to get trails in these cases even though that seems contradictory.  Remember - the digital camera is "interpreting" what the CCD sees, while film just prints whatever comes through the lens.

In this photo there are 2 light trail anomalies that were captured.  In this instance the sources are clear.   First, the LCD viewfinder from the camera the investigator is holding is causing some "ghosting".  This isn't really trailing but it is an example of what many people mistake for "ecto" or "mist".

The purple trailing in front of the stationary camera is actually the IR light.  Remember - we can't see IR light but digital cameras can.

This photo is showing us lots more IR light trails.  What is neat about this example is you can see the difference between the camera shake caused by the person taking the photo, and the shake/movement caused by the source of light.  You have 2 distinct IR beams causing trails in this picture.  The first is from a stationary video camera on a tripod.  All of the trailing from this is shake at the digital camera.  The trails from the handheld camera's IR light contain movement from both the digital camera operator as well as the handheld camera operator.

This photo shows us that IR lights aren't the only sources that can cause trailing.  In this photo the trails are caused by the record LED on a digital voice recorder.  As in the other cases, a slight amount of camera shake is all that was required to get the bright source of light to trail in the otherwise dark room.

This photo is a good one.  What makes this one different is that there is no source of light - at least not a readily apparent one.  In this instance the trail is caused by a reflection of the flash off of a shiny piece of decorative copper from a wind chime hanging in the window.  This photo is also a good example of how surface styles and object size can alter a photo.  In this case the edge of the piece of metal wasn't reflecting so as the reflection was imprinted there was a break at that edge, causing the "dotted" nature of the trail.

Light sources from within the room aren't the only culprits.  In this photo the light source is a street light outside the window.  The light was not shining through the curtain that much in reality so you are also seeing the cameras ability to pick up on low/non-visible light.

Conclusion
All of the above photos were taken with the same camera on the same night.  A post-investigation review found that the camera was not set properly.  It was set to "Night Photography" mode which seems like it would make sense to use however the slower shutter speeds and opened up aperture made it fall victim to the bright sources of light given off by the various LEDs and reflections.

We ALWAYS shoot with our digital cameras set to full auto.  This allows the camera to choose any option it feels necessary from it's full range of aperture, shutter speed and color settings. 

Specific settings will give you better photos in certain situations but auto will give you good photos in most situations.