A bug with version change

This is the bug:
I were on 1.8.1 and I had a lot of items, when I went on 1.7.10 with mods, I LOOSE ALL MY ITEMS!!

Step one to reproduce: in 1.8.1, in some chest, place items
2: go on 1.7.10 with mods and look at the chests.
If the bug is here, there is no enought items in the chests.

Please fix it fast