I think there's a bug with the download inventory feature.
If I download my whole inventory as a CSV file, the category column shows the
major category as well as the sub-category. Example: Parts / Minifigure Headgear
If I download my stockroom A inventory as a CSV file, the category column only
shows the major category. Same example: Parts (no sub-category)
But if I download all my stockroom inventory (A, B and C), the sub-categories
are back.