Boat mining slower than on land

When the player is sitting in a boat and mining blocks, the mining speed is significantly slower than the normal speed experienced on land (or when not in a boat). This slowdown occurs even when the boat is floating on the surface and the player's head is clearly above water (no air bubbles appear). The expected behavior is that mining should be at full speed when the head is not submerged.

I am not certain whether this slowdown is exactly the same as the underwater mining penalty, but it is definitely slower than normal. For example, mining sand (which normally breaks instantly) takes a visible fraction of a second instead of breaking immediately, which is not the case on land.

Steps to Reproduce:
1. Place a boat on water (any type).  
2. Get into the boat and make sure it is floating on the surface; the player's head should be above water (no drowning bubbles).  
3. Equip any tool (or use bare hands) and target a block that is reachable, e.g., a sand block near the water's edge or underwater but within range.  
4. Try to mine it and observe the break time.  
5. For comparison, leave the boat and mine the same type of block while standing on land (or on a solid block with head above water).  
6. Also compare with mining while fully underwater (if possible) to see if the slowdown matches.

Observed Result:
In the boat, the mining speed is slower than normal. For instance, sand (normally broken instantly) takes a noticeable delay before breaking. This happens even though the player's head is above the water surface. The slowdown feels similar to the underwater penalty, but I have not confirmed exact equality.

Expected Result:
Mining speed in a boat should be the same as on land when the player's head is not submerged, because the boat keeps the player out of water. Only when the boat is fully submerged or the player's head enters water should any mining slowdown apply.