Hi Nick,
I imported your view and I see the same thing as you. It's like the basis isn't calculating the contents correctly. I've seen this on other objects before, but labels is surprising. I think you should raise this as a ticket with IA Support.
The question is, is this an Ignition issue or CSS?
You most likely already know this but, as grow and shrink are both set to 0. The basis is essentially a fixed width. If you set a manual min-width then the basis: auto respects the children's collective width.
min-width: 100px
min-width: 90px
Also, when setting the children as basis: auto the parent container also starts to respect the contents width. It seems specific for a fixed pixels basis.