GV amount calculated twice

[plot0808]

I'm having this same issue:
http://www.zen-cart.com/showthread.p...2-times-v1-3-8
this thread is marked as duplicate but I can't seem to find the solved thread anywhere in the forum.
Can you point me where to look for or provide me with a clue about the solution?
The problem doesn't seem to be in ot_gv.php, because calculations are performed correctly. But in order total I see the gv amount doubled.
Any help will be appreciated! Thanks!

[plot0808]

Any ideas?