Losing enchanted items

Three times I have enchanted diamond pickaxes, put them into either my inventory or into a chest, only to have them disappear when I log back in. It has only happened when I do not first use the item before logging off. I am not using any mods. I have not tried this with any other enchanted items.
The first time I was trying to get a diamond pickaxe with a high level of efficiency and created three pickaxes with a durability level of III. I got tired of it and logged off for the evening and when I returned they were gone.
Not sure of what the exact circumstances were the second time....
Third time I created a pickaxe with an efficiency of IV for use the next day to dig a long tunnel and it was gone when I returned the next day.