I just tested it myself in 1.7.3 with 2.1.1 and was able to reproduce it.
Twice the items sucked out of the cart but half was ghosts. The ghosts seem to have prefered to go into the pipe while the real ones tend to just fall into the cart.
Here's the original report:
dyrewulf, on 25 September 2011 - 04:55 AM, said:
Has anyone else used obsidian pipes to extract items from a storage minecart? Using 2.1.1, SSP, I'm running into some buggy behavior, and I'm pretty certain it wasn't doing this when I played around with the same feature on the 1.7.3.4 version.
Basically the obsidian pipe, which is powered by a single redstone engine, is pulling out 2 items at a time. However, only 1 of those items is real, the other is a sort of "phantom" item. It's present, travels through pipes, can even be vacuumed up again by an obsidian pipe, but you can't pick it up when it falls on the ground, and it doesn't seem to insert into anything attached to the pipe.
If you watch the item count in the storage minecart as the items are being extracted, it's only decreasing by 1, but you can hear the double click sound of 2 items getting extracted, and you can see them hovering together when you watch the pipe. Standing at the end of the pipe, you get 1 item back, and 1 item drops on the ground and can't be picked up.
Now to add to this issue, this extraction pipe system is attached to 8 Better Than Wolves millstones. Only the real items(charcoal in this case) seem to be inserting into the millstones, the others hover on top of the millstone. However, when I checked the inventory of the millstones, the stack count was full(64 items) in 3 of them, but I only had 7 charcoal to begin with. I think some of the phantom items are being inserted, and those are getting full stack counts when they go through.
Just to clarify, I have no similar issues when items are vacuumed by the obsidian pipe when the minecart isn't present, it's just the minecart extraction that is bugged.