While a floating Fence or Wall block has a texture underneath, if you place a bell under said fence/wall, the block's bottom texture will become missing.
I think this occurs because the wall and fence think that the bell is a solid, opaque block, while in reality players can see past the bell and find that the wall/fence is missing a texture on the bottom. If the block above the bell is a fence, nothing will change if you connect it with another fence. However, if you do the same with a wall, the wall will regain it's bottom texture once it is connecting with another wall.
Another thing to note is that you cannot place a wall or fence directly above a bell. Instead you must right click on an adjacent surface to accomplish this.
Thank you for your report!
We're actually already tracking this issue in MC-148919, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.