[bobhenl]

Clicking the result (or cancel) slot of the anvil prompt closed the inventory inside the click event. The client kept its predicted cursor item, a copy of the input item, and in creative mode that item became real. Players got name tags (or the configured input item) in their inventory after answering a prompt.

• Cancel the click and complete the screen on the player's next tick (falls back to completing right away when the scheduler is unavailable).
• Call updateInventory() after closing, so the client drops any stale cursor/slot state.
• Same change in prompt-ui-26.1, 26.2 and 26.3.

Tested on a live Paper server: answering an anvil prompt in creative no longer leaves items behind.

[CyR1en]

The next-tick change looks right. Paper skips its normal sync when the menu changes during the click event, so deferring the close addresses the cause.

One small request: player.updateInventory() looks unreachable. cleanupScreen calls impl.close() first, so the player is back on their own inventory menu and the getTopInventory().equals(gui.getInventory()) check is false by then. That means the live test passed on the deferral alone. Could you remove the line from all three versions and drop that bullet from the description?

[CyR1en]

Went ahead and pushed the small cleanup myself so this does not have to sit around. I just removed the updateInventory() line in all three versions, the rest is your fix as-is. Thanks for tracking this one down!