For some reason, setting an Xkb keyboard for the first time doesn't work well inside FieldWorks. The keyboard is actually set (although it may take effect only after the first one or two keystrokes), but the indicator on the system icon bar does not change. Setting several Xkb keyboards at this point seems to fix the problem for when the first one is set different than the default keyboard. This hack is not guaranteed to work, but it does seem to help in most scenarios. See FWNX-1299.