Is this a bug?

I ran this command when a certain condition is met:
data modify block ~ ~ ~ Items append from entity @s data.FillerSpots[]

the block is a barrel, and the data it's getting is from a marker, the FillerSpots is just an Items array with knowledge books in slots: 1 , 4 ... etc, each with the tooltip display set to not show.
The issue is, whenever I run this command, every single item's tooltip in that barrel becomes invisible as if I modified their tooltip display to false. And the issue gets fixed alone if I stack an item on top of another, or if I just leave the gui and come back. No clue what causes it so I came to the conclusion that it's a bug. Though worth checking if anybody has any idea on what it is, or how to fix it.