(this time I use a translator)
Most likely this bug has already been found, and repeatedly, but here's a new versions, events were replaced by procedures. And in the meantime, it's still not fixed.
There is a GUI with 6 slots. Inside them through the procedure (Block Action) generated random items in random slots. Pick up these items does not work in any way. They just disappear when you try to use them or to place or simply take. I tried all possible solutions to the problem. For example changing the types of slots - input and output. Made in own inventory and inherited. To use the GUI for placing items in the slots but it's impossible because "guiininventory".
The point is not to ask you how to get around this bug, because it is impossible, but to ask when this bug will be fixed and whether it is possible to fix it at all. If it can be fixed, then I would do it as soon as possible and in the next update, because of this bug there is no point in the existence of your GUI system.
I know that the items can be pulled out in the creative, but mainly we do not make mods for the creative do we?
PS. I myself am a programmer, but in the field of game-dev so if you have time then I will not mind to know the detailed cause of this bug, if it is known.