Copy and paste does not work while editing the text of NSTextField controls in design windows

[gcasa]

Typing the keyboard equivalents Command-C, Command-X, and Command-V inserts the characters c, x, and v, respectively, instead of invoking the standard editing actions. Obviously, Command-A doesn't work either (cf. the respective bug report). I haven't looked into the source code, but it looks as if either editing text fields in design windows is implemented manually or the standard text field editor isn't first responder during editing.