I have found, a very simple solution
to obtain the true bounding box
of a simple insert that doesn't contain nested inserts.
The insert is not uniformly scaled, and rotated.
I explode it, calculate the Bounding Box avoiding hatches (and other "bad" objects)
then UNDO 1 time , and the result is correct . . .
It is not a matematical and elegant solution.
The solution is very limited by certain requirements that the block must have
However, at least, it works.
On the left side there is the result of LM:blockreferenceboundingbox
while on the right side there is the correct result that I get exploding it.
Ciao