Villagers cannot link to beds or workstations that are 5 blocks above or below them.

Steps to Repruduce:
Build a floor that is at least 4 blocks in the air. Now spawn a Villager on this block. Make sure that the Villager cannot escape.  Now build 3 blocks there from the floor on which the Villager is located. On these 3 blocks, place a workstation, e.g. a smithing table or a bed, so that the workstation or the bed is the 4th block.
You will notice that the Villager can connect to the workstation or the bed. 
Now dismantle the working station or bed. Build another dirt block instead. Now place a workstation or bed on this block so that the bed or workstation is the 5th block. You will notice that the Villager can no longer connect.
This also occurs if you place the Workingstation or a bed 5 blocks BELOW the floor on which the Villager is standing.
Expected Result:
The Villager connects to the working station or bed.
Observed Result:
The Villager does not connect to the bed or workstation.

Note:
If the villager is already linked to the bed or the workstation because they have previously been on the level of the respective block, then the villager will also find the way to the bed or the workstation, no matter how high or low the block is. However, this is strictly only if they are already linked to the bed or the workstation.

 
I discovered this bug when I started a large project involving villagers. This bug ruins the project. I believe this is a critical bug that should be fixed so that players can do more with the villagers,

I understand that there must be a maximum distance at which Villagers can connect with Working Stations or Bed. But max 4 blocks up or down is far too little. Villagers can connect to any working station or bed that is at their height as long as it is within 16 blocks. I think it would make sense to make a 16 block range up and down as well.