When does this usually occur?

mostly occurs when running long distances(happenend even very few times when walking small distances)

Does it happen when you cross another area and the map starts loading the next area?

it happens always when loading but the flashing is so random, today i experienced flashing while i was fishing.

I've aware of the issue but have no idea how it's currently occuring. There is already a client patch that should reduce the flashing although I don't see it working here since you've posted a bug report on it.

Any way to force the issue? You could maybe try the cache cleaner and see if it's happening more often or magically fixes the problem? http://emps-world.net/cleaner.php