It's intentional. Notice how one stack says "Fresh... ". The Qi quest does that to differentiate items which were made during the quest and which were already made before the quest.I’m not sure if this is a bug or a feature. I got the Java ring and, after killing a bunch of monsters I had a stack of like 90 triple shot espressos. I did the Qi quest to make some food and I made another stack of like 80 triple shot espressos. But the game wouldn’t combine the two stacks. And the blocking was different with the description. Once I completed the quest, I was able to combine my triple shot espressos.
Edit to add, I’m running Windows 11, single player, English.