Info from Official Mafia Wars Blog
Declaring war and helping your friends out with their wars is a great way to collect some awesome loot. Because the war loot is so awesome, we limit how much of it can be collected in a day to maintain game balance.
We have discovered that some of you have collected more than you should have. We will be reclaiming this extra war loot over the next few weeks. This will only effect non-giftable, tier 2, high-end war loot and above.
So, to recap: If you have collected more high-end loot from wars than you should have, we will be adjusting your quantity of that loot to what you should have earned within the appropriate limits.