(Originally reported over xJon/Tekkit-SMP#14)
Reproducible with only Thaumcraft and ThaumTweaks installed.

• Place a Warded Jar, and put some Essentia in it.
• Exit the world.
• Re-enter the world, and empty the Warded Jar completely.
• Break the Warded Jar, and see how it is now bugged.

The same report also mentioned this:

Issue 2 : Jars sometimes lose their name " Warded Jar" when used in infusion by being emptied and or being refilled or used as the recieving bottle of an essentia funnel or filling from a alembic. how to reproduce : (Seems to happen at Random from the previously stated interactions)

To help elaborate upon this issue, as I have also encountered it:

The issue happens to cause Warded Jars to gain weird NBT tags for an inexplicable reason upon saving the world.

It does not require any procedure other than saving the world with any number of warded jars being placed in the world for the issue to occur. It happens in any chunk regardless of dimension as well.