Steps to reproduce
Create a new world with the experimental feature Bundles in Creative Mode.
Open the inventory and get one bundle.
Insert some items in the bundle and watch the tooltip.
It does not show the inserted items, but shows its number. This worked correctly in 23w14a.
Code analysis
A code analysis by @unknown can be found in this comment.
(note: all class names are from yarn mappings, so keep that in mind)
This is a result of the new modifications to the DrawableHelper class. See the code utilized for rendering an item's tooltip:
Notice something off about it? It calls the exact same thing twice!
Now take a ponder at the interfaces available via the TooltipComponent interface.
Oops, looks like drawItems() was forgotten to be called 😞