Items that are Invulnerable become invisible when they burn

Put the summary of the bug you're having here

I wanted to make with /entitydata @e[type=Item,r=5] {Invulnerable:1b} an item Invulnerable.

but the item gets invisible and in the item falls 1 block in the ground!

1. make one Item Invulnerable with /entitydata @e[type=Item,r=5] {Invulnerable:1b}

2. make fire or lava in the item

3. now the item gets invisible and in the Block under it!