References #752, #857, FTBTeam/FTB-Modpack-Issues#6659.

The Worn Notebook has two entries on containment - one for the ritual and one for the jar. One of them is quite long. Neither mentions containing items, and I saw only one unqualified reference to containing "entities"; in all other cases, it's clearly specified that mobs are being referred to. In most cases, there's no mention of the broader word "entities" at all. Moreover, the JEI tooltip has the same issue: one unqualified reference to "entities", followed by conditions that apply to "[m]obs and jars" (not "items"). This has resulted in several bug reports, and quite a few confused players.

If this is indeed intentional, then you should update the documentation to reflect that. While you're at it, you should document the right click to remove items behavior.

On a related topic, you really should add a blacklist (with containment jars by default).

Observed on version 5.3.6, in the modpack FTB Evolution.