I caught an ink sac via fishing.
When I went to put it in the chest, the icon for the ink sac was dark (the icon was like when an item is in the furnace).
When I clicked on the ink sac, it then turned into this 99+ quantity ink sac (the icon turns into the normal ink sac icon) and it seems to be an infinite supply of ink sac.
Phone: O+ 8.37 Android
OS: 4.2.2 Jellybean
MCPE ver: Alpha 0.11.1
Note: 0.11.1 wasn't on the selection