Identical Arrays not identical

I have four Arrays that are indentical - [60,60]. I set each value in all four to True at the same time. I then set the same values to False at the same time:

For CountC = 1 To 553
    Local X, Y
    ReadData X, Y
    Shield1[X,Y] = False
    Shield2[X,Y] = False
    Shield3[X,Y] = False
    Shield4[X,Y] = False
Next

But when i access them it turns out that they aren't identical. 1 and 3 are identical, 2 and 4 are identical but aren't how they should be (because i'm plotting the True values and 2 and 4 have got a whole diagonal chunk missing from the image).

I have tried changing where they are but that didn't work and in the above code i tried to set it up as:

For CountC = 1 To 553
	Local X, Y
	ReadData X, Y
	Shield1[X,Y] = False
	Shield2[X,Y] = Shield1[X,Y]
	Shield3[X,Y] = False
	Shield4[X,Y] = Shield1[X,Y]
Next

But that didn't work either. After i set the False values i only access them to draw them so i can't see what's going wrong?

Can anyone help?