If you put a bundel into a bundle, it works.

If you now Right-click it with a new (empty) bundle, you get a bundle which should have 2 Bundles inside, but only shows one being inside. The "damage" bar underneath the bundle still goes up. You can also repeat this to increase the bar, while still showing 1 bundle inside.

If you empty these glitchy bundles, you can get your items back, so the items aren't lost.

If you hover the glitchy bundles over an empty bundle you can still fill it, although it doesn't show 2xBundles , instead it shows 1xBundle twice.