Addition of a SplitContainer on a Box doesn't show the SplitContainer [Cocoa]

[Dayof]

To reproduce this error I made this code https://gist.github.com/Dayof/1b1fcc8a4b463739a41919a77ee26d89 .

The following image shows the behavior of a SplitContainer inside a box:

The following image shows the behavior of a SplitContainer alone in a Window:

@freakboy3742's guess is that this issue found in the SplitContainer probably is because either the SplitContainer isn’t getting added, because something in the chain either thinks it doesn’t need to be, or it’s being set to size (0,0) because it doesnt’ know to expand to fill the available space.