The "Keep this window" dropdown menu in the "Adjust Effects" popover is broken in High Sierra (at least in macOS 10.13.4, which I am running). This was tested in Finder, Messages, and Preview, and appears to be a universal issue. The basic problem is that selecting either of the two options, "Afloat" or "Pinned to the Desktop", performs neither of these actions. If a window is already afloat by way of "Window > Keep Afloat", then the "Keep this window" dropdown menu in the "Adjust Effects" popover will display a new, blank fourth option selected instead of displaying the "Afloat" option. Selecting either of the two options, "Afloat" or "Pinned to the Desktop", while a window is already afloat returns the window to its regular state (the window will no longer be afloat, "Window > Keep Afloat" will be unchecked, and the "Keep this window" dropdown menu after closing and reopening the "Adjust Effects" popover will display the "Regular" option).
The "Keep this window" dropdown menu in the "Adjust Effects" popover is broken in High Sierra (at least in macOS 10.13.4, which I am running). This was tested in Finder, Messages, and Preview, and appears to be a universal issue. The basic problem is that selecting either of the two options, "Afloat" or "Pinned to the Desktop", performs neither of these actions. If a window is already afloat by way of "Window > Keep Afloat", then the "Keep this window" dropdown menu in the "Adjust Effects" popover will display a new, blank fourth option selected instead of displaying the "Afloat" option. Selecting either of the two options, "Afloat" or "Pinned to the Desktop", while a window is already afloat returns the window to its regular state (the window will no longer be afloat, "Window > Keep Afloat" will be unchecked, and the "Keep this window" dropdown menu after closing and reopening the "Adjust Effects" popover will display the "Regular" option).