When I am on my Experimental world (bundles turned on, obviously), and I get a bundle in my inventory, I have the ability to hover over it. For an empty Bundle, the UI says:{{{}
{}}}

Bundle

Can hold a
mixed stack of
items
[   Empty   ]

The "Empty" represents the bundle being empty, of course. However, there is this button for when you are in creative mode.

(X) Take from Bundle

This shows up when you hover over an empty Bundle too, for some reason, but usually this button clears your Hotbar, and as such when you press (X), it clears your Hotbar instead of taking something from a Bundle. When the Hotbar is cleared with a Bundle in it, I assume the UI assumes there's a Bundle in a spot where there isn't one. The empty Hotbar slot probably does not have a Bundle fullness value because it is not a Bundle, and as such the UI gets confused as to if the Bundle is full or not, showing:

Bundle
Can hold a
mixed stack of
items
[   EFqlly   ]

The "EFqlly" text is a representation of the "Empty" and "Full" text overlapping, and does not perfectly represent what the text is shown as in-game. The space between "Bundle" and "Can hold a" has also been removed, making the UI shorter, the fullness meter is overlapping with the "items" text, and is also red, as if the "Bundle" is full. The description for the Bundle is also shown regardless of if the deleted Bundle had items in it or not.

Here is an image i screenshotted (using the Nintendo Switch capture button because I forgot that Minecraft let you screenshot and I don't know if it lets you screenshot inventories) of the glitched Bundle.
[image removed, please look at attatchment]

I think this is a pretty funny bug because I discovered it in less than an hour of using the Bundle lol