When changing sliders and such, many network game messages are sent, resynchronizing everything.
This is quite slow.
This waits at most 400ms second before sending a message, avoiding flood. The behaviour is to send a message even if other changes are coming, to avoid a situation where many changes regularly would never trigger a network message change.
(D3243 will make it possible to send partial updates, which ought to alleviate some of this).
Reported by: nani