I've been doing a little cheeky creative mode to quicken the process of chiseling some details in my survival world.
While doing so, I accidentally moused over a long chest and destroyed it with a click. When I went to investigate, I heard myself picking up all of the items from the box. The box was entirely full, all slots in use. There was no way my inventory could hold all of that material. I switched over the Survival mode to check my character's inventory, and I had only a fraction of what was in my original chest, because that's what my character could carry.
Where did all the excess stuff my character 'picked up' go? Is it gone? As far as I can tell, there is no secondary personal inventory while in creative mode that I can check. If it's gone, that sucks massively and the game should not allow for you to pick up items/material in excess of what you can hold, even in creative mode.