I am experiencing a slightly different bug in ArcGIS 10.5, but which wasn't an issue with 10.4 and before. When in the Layer Properties dialog box, in the Symbology tab, I can right-click the colors/symbols to show the various context menu options ("Flip Symbols," "Ramp Colors," etc.), but when I select "Properties for All Symbols...", ArcGIS 10.5 doesn't respond. The work around for now is that I can manually select all symbols, and then select "Properties for Selected Symbols..." from the right-click context menu, and that works...
Strange for ArcGIS 10.5 to have this and other bugs...