Bug/Issue Retaliation value not showing (Merfolk vs Sea Turtle)

I was on my first water battle in the campaign, and I found a bug involving the Merfolk.
I tried to recreate the situation in my own map, and it happened:

When you move a Merfolk from a Ground tile to a Water-related tile to attack a Sea Turtle, it doesn't show that the Turtle can and will retaliate, when in fact, it does.