Hi itma
You definitively have a peculiar stamp there, although W.C.G. McCracken had used John Ash's plates (the former printer), the faulty plates of the original 3d that has those errors were destroyed before McCracken came onto the scene. The truncated "T" was on the 1937 plates and the stamp you have was printed in 1941.
But your stamp definitely shows some sort of truncation; I have looked in the recently published Australian Commonwealth Specialists' Catalogue (2015), and it shows no mention of the brown 3d having such a variety.
Just my opinion and what I can just make of it, there is a discolouring in the background, I'm not sure what may have caused it, but it might have been the cause of the "T" becoming truncated; you can also see a mark crossing half-way through the "T".
I've enlarged the image to show the discolouration.
I'm very curious, I'll be forwarding the image of your stamp to a friend of mine; he and his brother are internationally renowned experts on Commonwealth pre-decimal stamps, especially pre-decimal Australian (over 30 years experience).
I will get back to you by the end of the day with what my friend makes of it.

Discolouration in the background
Stamp on the left does not have the discolouration in the backgroundRob