I noticed some of my primary inventory items had disappeared on day one of 1.0.4.1 after a long session of testing trading.
As there are several long standing bugs causing loss of items in one way or other (definately NOT MCPE-15010 happening here!!), I didn't report until I got time to recreate it with meaningful info.

Recreation:

• Using PE GUI
• In a single session without exiting the villager trading GUI.
• Librarian offering 1 emerald at cost of 25 paper.

Shot1 Inventory before trading: Note slots 1, 2 and 3.

I cant be sure of the exact additions and trades order as I was fiddling
and watching how the gui behaved but essentially I was just stuffing the
input with as much paper as I could, to 64 obviously, then trading as much
as possible, then topping the input up again by long pressing a full stack
to refill the input slot. Kept trading until the villager locked out the offer.

Shot2 Inventory after trading.
Note that contents of slot 1, 2 and 3 have been overwritten with paper contents.
The original content of Cooked Pork, Steak and Mutton have disappeared.

Observations:
I noticed the following, if for example..

• I loaded the 43 part stack of paper into the input slot.
• Trade one emerald.
• I have 18 paper in the input slot (offer is 25)
• Long pressed a full stack in invetory to fill input slot to 64 (46 transfer to input slot, then input slot stops incrementing at 64)
• Release the long press.
  • At this point the GUI animates a movement from the long pressed slot to some slot towards slot 1.
  • As I was TopUp/Trading repeatedly this happened on each top up so several times in total over the trading session.
  • This correlates with the number of inventory slots overwritten and items lost.

I think the overwrite/loss is happening here while reshuffling the remainder of the long pressed slot back into inventory once the slot is filled and the long press subsequently released.

Other Info:
Villager Spawn Versions..
Not sure if this is a factor..
I'm not sure on what version all of the villagers were spawned some may have been as far back as 0.14.
Many of them were "born" and raised on 1.0.4/1.0.4.1 as I have been breeding and selectively culling the villagers to shape the professions of the population and improve randomized elements of the offers.
I can post villager NBT data From MCPEViz logs if it helps debug.