Can't switch between hotbar slots while displaying experimental UI

The bug

Can't switch between hotbar slots while displaying custom UI using scripting api.

Other controls(e.g. walk, look around, break/place a block) are available.(Only switching hotbar slot is not working.)

To reproduce

1. Prepare resource pack containing html file in experimental_ui folder.

2. Prepare behavior pack containing scripts.

   // display UI
   let loadUI = this.createEventData("minecraft:load_ui"); loadUI.data.path = "example.html"; loadUI.data.options.absorbs_input = false; loadUI.data.options.force_render_below = true; loadUI.data.options.is_showing_menu = false; loadUI.data.options.render_only_when_topmost = true; loadUI.data.options.should_steal_mouse = true; this.broadcastEvent(loadUI.__identifier__, loadUI);

1. Create a world, and activate resource/behavior pack, also enable "Use Experimental Gameplay" in settings.

2. In the world, can't switch hand holding item while displaying custom UI. 

My English is poor, sorry😞