The `java.nio.channels.Selector` API specifies precisely how selection operations add selection keys to the selector's selected-key set or update the readiness information of selection keys already in the set. The `Selector` implementations in the JDK did not historically implement the latter correctly, meaning that the readiness information was overridden and previous readiness information was not preserved for cases where a channel is selected and its key was already in the selected-key set. This issue has been fixed in JDK 11. This behavior change may surprise code that invokes `select` (or `selectNow`) and doesn't process keys added to the selected-key set before performing another selection operation.