The Wayland core protocol has described surface state updates the same way since the beginning: requests modify pending state, commits either apply that state immediately or cache it into the parent for synchronized subsurfaces. Compositors implemented this model faithfully. Then things changed.
Buffer Readiness and Compositor Deviation The problem emerged from GPU work timing. When a client commits a surface with a buffer, that buffer might still have GPU rendering in progress. If the compositor applies the commit immediately, it would display incomplete content—glitches. If the compositor submits its own GPU work with a dependency on the unfinished client work, it risks missing the deadlines for the next display refresh cycles and even worse stalling in some edge cases.