why isnt math.random random ?

Alright so this code assigns random images to imagelabels and it works but however when you rejoin the game you can see that it is the same images in the same order.

math.randomseed(tick())

for spin=1,100 do
	wait()
	y = Instance.new("ImageLabel")
u = (math.random(1,100)*100/100)
if u < 33 then
	y.Image = 'http://www.roblox.com/asset/?id=851659838'
else
	if 33 < u and u < 66 then
		y.Image = 'http://www.roblox.com/asset/?id=171155237'
		else
	if 66 < u and u <= 100 then
		y.Image = 'http://www.roblox.com/asset/?id=102106311'
	end
	end
end

Try using elseif once in a while

math.randomseed(tick())

for spin=1,100 do
	wait()
	y = Instance.new("ImageLabel")
	u = math.random(1,100)
	if u<33 then
		y.Image = 'http://www.roblox.com/asset/?id=851659838'
	elseif u>=33 and u<66 then
		y.Image = 'http://www.roblox.com/asset/?id=171155237'
	elseif u>=66 then
		y.Image = 'http://www.roblox.com/asset/?id=102106311'
	end
end

Your script was messy and that could cause an unnoticed problem because you cant really see what direction its taking