Slight flash in luminance with fade-in dissolve

Firstly, I checked the FAQ and found nothing.

On DV footage I digitized at 8 bit>DV, I set a
simple fade-up from black on the timeline
on the clip.

It appears that the luminance will flash during the transition
of the clip; and it does this whether I use a dissove or animate the
opacity of the clip.

It is driving mr crazy, can any one help?

Also, I just noticed this; but when the video is in pause mode the
luminance seems about 10 per cent brighter than when in play mode.

Once the playhead starts moving the luminance will drop to what I assume
is the correct levels.

Quite odd