If a player give themselves a potion that has the "ench:[]" tag, the potion doesn't show the enchanted glint like other potions, however, the name of the potion is blue indicating that it's enchanted. The same is applied to the Water Bottle, Awkward, Mundane, Uncraftable, and Thick Potions respectively.

The first two screenshots show the two potions with the right being a regular black potion, and the left being a potion with the "ench:[]" tag. They are black as to make the them more visible. As the last picture is the two of them side by side, with the potion tab opened for reference. The bug also applies to the splash potion and lingering potion counterparts.

This is weird as I'm pretty sure this worked in 1.8 (Please confirm).

Many other items don't seem to have this issue with the "ench:[]" tag.

/give @p potion 1 0 {Potion:"minecraft:water",ench:[]}