Describe the bug
I use multiple colours of the TravelersBackpack [T/B - from here on] & change their colours (ie. 'v1.12 Abilities') to differentiate between them.
When I remembered that the T/B has a crafting grid I used it to change a standard T/B to a T/B-redstone - but because you can not place a T/B into a T/B the recipe either trashed/erased my T/B or the items used in the recipe.

To Reproduce

1. open a T/B (either from the hand or worn on back);
2. hover over a block of redstone & press "U" (default for JEI "Usage");
3. if all items are available in inventory, press the "+" (plus) button to add recipe into the T/B crafting grid;
4. the 'standard' T/B does not show in the centre of the crafting grid for the recipe nor the output of the recipe;
   
   

but both bags are there, however:

• if I click the output a 'standard' T/B is the result & my all my items in the recipe are gone/used without giving me my 'redstone' T/B;
• if I exit/escape the GUI I will lose my 'standard' T/B that is in the centre of the recipe (ie. I lost the 'standard' T/B used in the recipe, along with everything in it)

Expected behavior
Either the recipe completely fails & I need a vanilla crafting table to make T/B colour variations ('v1.12 abilities'/colours) or I get my BrandSpankingNew redstone T/B

Screenshots
Posted up above in the 'steps' step

Required informations (please complete the following information):

• Mod version: TravelersBackpack-1.16.5-5.4.1.jar
• MC ver 1.16.5

Additional context
... ask & ye shall be answered...

That may be the issue with JEI

Have you tried reporting this issue to JEI author?
Because there must be some kind of issue on their side I think. The backpack can't be put in backpack inventory, but it moves it anyway.

No I have not. I thought it was worth mentioning here though but I no longer worry about it since I now know to avoid it - only the first 2 times it happened really confused me so I made a copy of my savegame to see why/what happened & if it was reproducible.

I only use 4 bags at most so its easy to work around it.

I'm not sure if you'll get this message but I've restarted a game & am using 'CraftingCraft' mod {it's a portable crafting table} & JEI is doing a similar thin but it dupes {duplicates items} rather than making them disappear - so you maybe onto something about JEI causing the issue.

I've used 'CraftingCraft' much longer than your mod & I've never noticed the duping before [coz it neva happened]...

I'll try older versions of JEI & update this thread if need be - & I'll make a JEI Issue if tests show a difference.