When the bundle is in the inventory, you can see how full it is by a blue (or red) bar, which is similar to a durability bar. When an item with a durability bar is inside a bundle, you can see the durability bar next to the item inside the bundle UI, as expected. When a partially filled bundle is inside another bundle, there is no blue bar below it in the UI.

Steps to reproduce:

1. Grab 2 bundles
2. Put an item into the first bundle
3. Put the first bundle into the second bundle

Observed result:
When hovering over the second bundle, the first bundle's fullness bar does not appear.

Expected result:
The first bundle's fullness bar appears.