Items Vanishing

I opened 1.8 just to go looking for bunnies then decided against actually looking for them and went back to 1.7.10. When I returned to 1.7.10 all the item in my inventory and in my chests, including ender chest, were gone.

I'm not to upset as I only lost some horse armor and a diamond pickax but y'all might wanna check into this.

Much appreciated DBL