Look at the hello world tutorial example:
It creates a vertical box with a text and a button, and the text is center-aligned both vertically and horizontally:
efl_gfx_size_hint_align_set(efl_added, 0.5, 0.5)
However, it is only centered horizontally. Using Clouseau, you can see that the text widget uses up all the available vertical space, so there's no room for it to align.
If the box is made horizontal, the problem is reversed: The text is correctly aligned vertically, but not horizontally.