By putting items into stacks of presents you can duplicate those items.
Steps to reproduce:

• Create at least 2 presents
• Put both as a stack into item slot 1 and use them
• The present GUI opens. Here you can insert some precius gems and stuff into the present
• Close the present and go to your inventory
• Right click (drag) the presents stack through your inventory to split that stack
• Now every present should contain the same stuff

Minecraft 1.8, Forge 1563, cfm 4.0.1, SSP, probably also SMP

Fixed in f9b667b