Editior Base Font shown as "(null) -0.0"

The font of the editor cannot be changed, and in the preference panel the Base Font is shown as "(null) - 0.0". If I click "change" button and select one font, nothing happens. Currently the font of the editor is Arial, the default font. Does anyone know why this happens, or which file controls this setting?

Start by reproducing the preference-panel behavior described in the issue and trace the editor's Base Font setting from the preferences UI. Done means selecting a font updates the stored preference and the editor display, with the value no longer shown as "(null) -0.0".

Written by the indexing model from the issue text.