https://github.com/zkoss/zkspreadsheet/blob/0811b0687adb71288a3c976e5010ea9cc46a707e/zss/src/org/zkoss/zss/api/model/impl/EditableFontImpl.java#L61
It seems a bug that copyAttributeFrom() doesn't copy the properties below:
private boolean overrideName;
private boolean overrideColor;
private boolean overrideBold;
private boolean overrideItalic;
private boolean overrideStrikeout;
private boolean overrideUnderline;
private boolean overrideHeightPoints;
private boolean overrideTypeOffset;