The alpha channel transparency behavior masks older objects while allowing newer objects to be seen.
In other words, If you create a Cube first, then a plane with alpha transparency the plane masks the cube from view.
if you create a plane with alpha transparency then a cube, the cube is not masked.
If you create a Cube first, then a plane with alpha transparency the plane masks the cube from view. Then if you duplicate the cube, the duplicated cube is not masked. Then if you duplicate the plane, it masks everything again.
In the attached example, Cube was created first, Then Plane, Then Cube.001, Then Plane.001, Then Cube.002.
Additionally, behavior changes when objects are selected. In the above described example no objects are selected. Selected cubes are always masked by planes with alpha transparency. Selected planes never mask cubes.
It looks like there was an attempt at some point to remedy this problem by adding Object data Display Transparency option. However this has other undesirable consequences like elimination of the selection outline.
The default behavior is illogical. Requiring objects to be duplicated in the order that you want them shown is not logical. The behavior changing depending on object selection is also illogical; why would you want an object to disappear when it is selected?