Full bundles still show the blue progress bar unlike when they are first introduced. It is not mentioned in the changelog. From bugsbugsbugs's video, it appears the bundle progress bar when completely full in 20w49a+ is the same as having 63 items in a bundle in 20w48a-.

How to reproduce:
1. Get a bundle.
2. Put an unstackable item inside of it.
Result: The blue bar is still shown.
Expected result: The blue bar won't be shown.

Why is this a problem?
Full bundles and empty bundles have very different behaviors, namely you aren't able to put any items inside of a full bundle. With this behavior, players cannot tell the difference between a full bundle and an almost full bundle without hovering over it, despite them working quite differently. It is good design to make different behaving things visually distinct.

Yes, from bugsbugsbugs's video it is shown that adding the last item extends the progress bar one further to show that it is full, but it is still not as distinct as 20w48a. Players glancing at their inventory usually cannot tell the difference between almost full and full bundles in real gameplay scenarios.