Flipped image using "slice"

I have a 3D volume dataset in X-Y-Z. Now try to use SLICE with SURF and ROTATE to get a diagonal cross section. But I found that the images are flipped using X'-Z' and Y'-Z' (say X'-Y'-Z' are rotated coordinate system). What was wrong then? Thanks.

[Adam]

It would help if you post some code. It's almost impossible to say what is wrong in a theoretical case without some example code we can run that shows the problem.