I have the same unit and it does not flash.
Are you in very shallow water when it flashes the depth or does it do it all the time?
From looking at the manual http://www.uniden.com/pdf/QT206om.pdf
it would appear that it should only flash if there is a problem with the sensitivity adjustment but then it should only flash a specific number and not the correct depth.
Is there any chance you have the alarm set and it's causing the screen to flash?