Emeus Constraint Layout does not play well with nested layout inside GtkGrid

[rmacqueen]

I have: EmeusConstraintLayout --> GtkGrid --> EmeusConstraintLayout

Under this setup, widgets (specifically, GtkLabels) added to the inner EmeusConstraintLayout are not arranged properly - indeed they seem to not show up at all. However, if I substitute the GtkGrid for a GtkFrame, then everything works as expected.

Minimal example: https://gist.github.com/rmacqueen/2799077115ef59cbd7e187c2fccd8c73

In this example, labels (added to inner, nested layout) will not show up at all. However, if, on line 10, you replace GtkGrid with a GtkFrame, then you get the desired result.