Creative mode
I discovered that one when I drop some items from my hotbar to the trash to clean it. And I saw some rail speed controller wandering in space while I hadn't touched them during this session.
I understood then when I open my inventory in creative and attempted to split an item in it.
{F7733}
If you click on the red zone nothing happen, but if you click on the green one with the **right click**...
{F7735}
...it'll open the split menu of the item in the background (in the inventory menu) behind the actual split menu.
{F7737}
All that part above was reproducible. But not the following one which occures right after :
I had of course close the split menu of the speed controller. And then click on **cancel** in the split menu of the **teal light** but this happened...
{F7739}
Each time I click on **Cancel** a new split menu of the same item popped-up, I could made them pop-up infinitely (I made 5~10 times) until I click on the **red cross** and closed the window but then guess what...
{F7741}
Rail enhancer blocks decide to leak from invetory anyhow (mostly when I moved the bugged split window from above the invetory to outside)
Logs: {F7743}, {F7745}, {F7744}, {F7746}, {F7747}