MCreator issue tracker has been migrated to GitHub.
Existing tickets have been migrated to GitHub. Please open new tickets on the GitHub tracker instead. If you do not have a GitHub account, all feature requests and bug reports from forums are still considered and checked by the maintainers.
This is a known issue. Right now only working inventory is the one you bind to the block. This bug will be fixed in future updates.
I suggest you to check our wiki page on how to make GUIs with slots for now: https://mcreator.net/wiki/making-guis-slots