I've just built a villager swapper similar to Docm77's, but now that I've put the villagers in the slots, I can't trade with them. Once I have swapped them down and up once, the trade window appears for a split second when I right click on the villager, but disappears immediately after. I've removed the blocks above them as well as in front of them, so they shouldn't be obstructed by anything, but to no avail.
I was able to get the trades back with one of them, by pushing him around in his cell. Is this then due to the villagers being partially inside the glass or something? How can I fix this?
Below are pictures of my setup.