A scan of a high contrast film such as Kodachrome results in haloes around bright areas adjacent to dark areas:

Scan with halo around bright areas

Contrast enhanced to make flare more visible

Cause(s):

1. This is flare, inherent to the CCD technology used by consumer scanners.  Flare is also present in the mid-tones as reduced pixel-to-pixel contrast.
2. Dirty optical element

Remedies:  1. Decrease analog gain.  2. Create a mask of bright areas, perform scan of masked image, perform scan of bright areas, and composite scans.  Film masking   3. Use a drum scanner.  4. Clean optics

Comment: Unlike other types of flare, such as that caused by dirty optics, CCD flare varies with the scan traversal direction.  That means an image created with the traversal from a bright to a dark area will differ from that done with the traversal from a dark to a bright area.  Over aggressive use of analog gain can also aggravate flare.

I've found the LS-9000 to be a clear improvement over the LS-8000 and previous generations of scanners in controlling flare.