[1.4.6][SSP] Felling turtles destroy blocks they shouldn't be able to

STEPS TO REPRODUCE
1. Craft a Felling Turtle (Diamond Axe + Turtle) and a Digging Turtle (Diamond Shovel + Turtle)
2. Place the Felling Turtle and Digging Turtle in the world.
3. Place a block they shouldn't be able to break (such as obsidian) in front of them (or above or below)
4. Run lua, enter "turtle.dig()" on both (or turtle.digUp() or turtle.digDown())
5. Observe the output, and what happens to the target block

RESULT
The felling turtle breaks the block and destroys it (does not appear in inventory), returning "true"
The digging turtle does not break the block, returning "false".
This is inconsistent.

EXPECTED RESULT
Primary expectation is consistent results. Either both should break their blocks, or both should not.
Functional expectation is that both the felling turtle and digging turtle should not break the block and should return "false".

ADDITIONAL INFORMATION
See demonstration at:
[media]http://www.youtube.com/watch?v=sW1Go-TBiZ8[/media]
(Includes Felling Turtle on the left, Digging Turtle in the center, and Mining Turtle as control on the Right)

I think it's intended at the moment. They're currently equivalent to mining turtles except they do more damage in combat.

(Edit: I didn't see that it destroyed the block)

Strange - they both should destroy blocks. I'll speak to dan.