Sniffers seem to prioritize grass blocks over podzol, mud, and muddy mangrove roots, even if the grass is outside of a fenced or wall in area and there is no may to pathfind to it.

To recreate

1. Put a fence or wall around a 15x15 block area of podzol, mud and muddy mangrove roots, with grass blocks outside of the fence.
2. Place one or more sniffers in the area. Wait a few minutes.
3. Replace 4 blocks in the middle of the pen with grass blocks. 

Expected result: Sniffers should prioritize eligible blocks they can pathfind to when searching.

Observed result: When the sniffers search for seeds, most of the time they will sniff to the fence, then stop searching. After you place grass blocks in the middle the sniffers will dig in these 4 blocks before any other block in the pen.