Melon & pumpkin stems only connect to naturally grown melons & pumpkins

Melon & pumpkin stems will connect to their respective blocks if they naturally grow it as expected. However, they will not connect to manually placed ones.

How to reproduce:

1. Plant a melon or pumpkin stem on a wet piece of farmland.
2. Let it grow or grow it with bonemeal.
3. Wait for its plant block to grow next to it. The stem will connect.
4. Collect the block and place it back down manually. The stem will not connect.

Expected result:

The stem connects to its respective plant block.

Actual result:

The stem will not connect to any other blocks than naturally grown ones.

 

The most prominent use of connecting stems to manually placed melons or pumpkins would be building a garden, having the stem not connect is visually displeasing.