When switching between different fill or line symbol types in Symbol Property Editor all user customization is lost. ArcMap mindlessly overrides all user defined settings favoring default symbol.
Picture below shows current ArcMap procedure of Symbol Type change: customized Line Fill Symbol Type with Cartographic outline switched to Simple Fill Symbol and back to Line Fill Symbol.
ArcMap should preserve all user defined symbol properties when choosing different Fill Symbol Type or Line Symbol Type. Concurrently ArcMap should keep temporarily in memory all previously customized Symbol Types (within edit symbol session) in case the user wants to revert back. Finally, ESRI should at last introduce Undo/Redo functionality within Symbol Property Editor.
Picture below shows proposed ArcMap procedure of Symbol Type change: customized Line Fill Symbol Type with Cartographic outline switched to Simple Fill Symbol and back to Line Fill Symbol while keeping all customized symbol properties.