[Bug-Win] [0.9.112] Exploration and borders

[simpkin_11]

3 Followers explore a region:

Turn ends: I receive messages that

Follower 1: Explored 1 tiles
Follower 2: Explored 2 tiles
Follower 3: Explored 2 tiles

Total=5 tiles

On the map I notice the fog of war was removed from 5 tiles
4 inside the borders of the explored region
1 outside the borders in the water.

A few turns later:
all of the tiles inside the borders of the region are visible, half the tiles that were hidden are now visible.
Event received that exploration is complete and I should give the followers another task.

At this time I am unable to explore further in this region, but not all of the border regions (across the border but touching) are visible.

I cannot set followers to explore a region that does not have at least one visible tile.

With the current example I am seeing this with a region bordered by ocean, and there are visible ocean tiles to explore in the neighboring region (ocean)

My interest is; if it is possible to get a result where there are no border tiles visible, therefore not be able to send followers to explore a neighbors region?

Is it expected that followers will sometimes explore tiles across a border, while exploring?