When right-clicking a command block on y = 255 (only seen on chain command blocks) with a command set on the top face, a command block GUI with no command set appears.
Additionally, the "Max building height is 255" message is displayed, despite the lack of placing attempts.
Environment
Windows 10
Resolved this as duplicate of MC-126830 despite it being a duplicate itself because the fact that the GUI opens is a little bit special.