Item duplication via portals

Video Proof: http://youtu.be/D16dWcR9cXE

Steps to reproduce:
1] Setup rails & portal as seen in video
2] Place minecart with chest on rails
3] Put item(s) in chest
4] Push cart towards portal
5] Take item(s) out just before / as it enters the portal
6] Place item(s) in chest
7] Go through portal and collect duplicated items
8] Come back through and collect previous items

NOTES:
I have set this issue as PRIVATE as it does contain what I feel to be sensitive information. Duplication glitches can destroy server economies.