character display style changed after installing a new font

When the current selected font is missing glyphs for one or more specific characters, then Qt will try to find a fallback font for this or these particular characters (the found fallback font must containts the appropriate glyphs for characters). But based on this, when user install a new font which is also contains another appropriate glyphs, the Qt may changes the previous fallback font to the new one automatically, and this behaviour would lead to the character display style changed without the actually user operation.

Please check my attachments, the picture 1 shows that before I installing a new font, after I installing a new font, the charcters is changed to the state of picture 2.