Currently, setting RadSpellChecker.WindowSettings.ShowAlertWhenSpellCheckingCompleted only partially affects the "All at once" spell checking scenario. It is used only to suppress the alert in cases when there are not spelling errors in the control. Instead, it should be used to suppress the informational message at the end of the spell checking process and automatically close the dialog. Workaround: Create custom spell checker class, similar to RadSpellChecker, which automatically close the dialog (see the attached project).