Hi! 

I did these steps:

1. Place Lectern and let villager take a profession (when offer is good then point 2)
2. Trade with villager one or two times
3. Change villager into a zombie villager
4. Cure zombie villager

Villager sometimes had old offer with discounts, but sometimes he had different offer than before (with discounts too). This bug doesn't appear  when I destroy Lectern straight after point 2 - he always had an old offer (I checked it 9 times).

I notice that sometimes when villager changes from a zombie villager to villager for a moment he is without profession. I share video with that moment below.

Sorry for my English.

Best wishes.

KasesbianPL