Reproduction:
-Find and successfully trade with a villager.
-Wait for the regen/green particles to appear.
Result:
The villager doesn't immediately unlock the next trade when checking the first time, but after checking again the villager does unlock the next trade. This also happens when successfully trading the newer trades as well.
Confirmed. This has happened to me since the Win10 exploration update 1.1. After trading the last possible trade, (initially the first enchanted book trade) I exit the trading menu and wait for the green and purple particle effects to show, then go back into the trading screen and advance to the last possible trade (bookshelves). I am still locked out of the next series of trades until I exit the trade screen and enter again. Only then are the next set of trades available (glass blocks). This happens for every type of villager the first time through. I am on the Win 10 platform.