I'm not certain whether this is really a bug or not, but I wanted to post this here just in case. I used the /tag command to add a tag to an item I threw on the ground. I ran a say command as the item using "/execute @e[tag=name] ~~~ say hello", and it worked. Then I picked up the item, and threw it back on the ground, and the execute command didn't work anymore because the tag was gone.