I am completely unable to get villagers to mate, no matter how many doors I build they never get hearts over their heads.

See the attached pictures for my test setup. There are exactly two villagers in the entire village in both pictures. I gave both villagers a few stacks of bread.

On 18w07c no hearts appear, no matter how long I wait. Reading the entity data of the villagers also shows that they are unwilling (data get entity @e[limit=1,type=villager]).

On 1.12.2, I see the first hearts after not even waiting for a minute.