The Bug:

Bundles cannot be undyed using Cauldrons filled with undyed water.

Steps to reproduce:
1. Hold a dyed Bundle
2. Use dyed Bundle on a Cauldron filled with undyed water

Expected result:

Dye from bundle is removed.
Actual Result:

Nothing happens.

Feedback Site Link:

baslod made this issue Invalid, so it is on the feedback site:

https://feedback.minecraft.net/hc/en-us/community/posts/30491953847821-Allow-bundles-to-be-undyed