When a spash potion lands on a block, the particles always come from the north-west corner of the block. This happens in a ton of versions, going all the way back to 1.8.1 and possibly earlier, but for some reson the bug tracker won't let me add them.
Environment
Windows 10, No OptiFine
This issue is a duplicate of MC-45749. Please search before reporting issues (if you haven't already) to see if your bug has been reported before.