Bounding Box - intended effect or bug?

Hi, I’m a student using cubit and I was trying to use the boolean selection functions in cubit, ie

select vol with x_min > 15

However, I seems to me that the object I was trying to select has an x_min that is different when compared to the actual geometry. I expected the above line of code to just select the triangle (vol 4), however, it does not seem to do this.
I also applied an extended bounding box (see blue wireframe parallelepiped in figure) and found that this creates a different shape and size bounding box than I expected. Is this the intended effect? When I create a tight box I do get a real bounding box as expected. I was wondering if this was potentially a bug, or if I’m missing is a setting I need to change to use the tight bounding box for x_min and x_max etc…


I also added the cub5 file.
error.cub5 (848.5 KB)
Thanks in advance!