This is happening to me too in the current version (1.11.1) of Minecraft PE. If you place an item on armor stand and then you give the armor stand invisibility, the item the armor stand is holding will float in front of you. If there is another armor stand, the item will teleport to that armor stand. If you destroy that armor stand, the item will continue to follow you. Really annoying when making maps.
@CJC it has been confirmed for a while now, but they still haven't fixed it. I'm also having the same problem with armor. When you place armor on the armor stand, then give the armor stand invisibility, the armor also becomes invisible.
Playing on a Acer B1-850 tablet
I'm happy to say they have finally fixed this bug in the new beta version (1.13.0.1)! 😃