Qt unable to render glyphs with large x/y/width/height correctly with sub-pixeling enabled

In QFontEngineFT::loadGlyph(), the condition for bool large_glyph is only judged in the else case for useFreetypeRenderGlyph, which causes the glyph info to be always stored into defaultGlyphSet in a new Glyph struct, that uses only single byte for x/y/width/height/xOff. This results in wrong bounding boxes returned for large glyphs, and thus crippled (clipped/chopped) rendered glyph pixmaps, as illustrated in attachment with comparison with correct renderings.

A workaround is to set subpixelType to none by changing Xft.rgba value to none, e.g. executing echo Xft.rgba: none | xrdb -override

However, it seems reasonable to consider this behavior of Qt a bug, as it cannot present correct glyph without sub-pixel rendering disabled.