my SP worlds wont save!

i was playing on my SP world and i went to the nether to collect nether quarts. i got some and put them in a chest. (the chest was half full of them) i saved and exit. and when i re-opened the world my chest was empty... and the quarts from the nether (i mined) where gone. so i could not get them back.

Steps to Reproduce:
1. load a world
2. put items in chest, break blocks, ect
3. save and exit. then re-open world