HI!
when working with persp on,we can’t get the correct result,such as masking,cliping…see the jpg below:
thanks for helping
So what’s the problem??? 
Why are you doing that with perspective on anyway? That should be done in an orthographic view. The solution is easy…turn off perspective. 
COZ i HATE orthographic view
:evil:
PERSP VIEW look more natural…
:lol: