[Freetype] bytecode interpreter makes antialiased text worse?!

[Ben Liblit]

Red Hat 8.0 ships a GNOME2 environment that uses FreeType 2.1.2 for most
text rendering.  (Yay!)  Their standard FreeType build *disables* the
bytecode interpreter.  While text is rendered antialiased by default,
non-antialiased text clearly looks a bit lumpy without the bytecodes to
help smooth things out.

I decided to rebuild my FreeType with the bytecode interpreter enabled. 
Non-antialiased text looks much better.  However, I was surprised to
observe that antialiased text looks significantly *worse*.

Consider the two small images attached below.  The first,
"no-bytecodes.png", shows some text rendered by a GNOME2 panel menu
without the bytecode interpreter.  Contrast this with the second,
"bytecodes.png", taken with the bytecode interpreter enabled.

When the bytecode interpreter is turned on, notice that several 
rendering anomalies appear:

   - Several letters are narrower, giving the whole run of text a more
     compressed feel.  This is especially noticeable in "R" and "o".

   - The left side of the "Q" is painted in too light a shade of grey,
     causing it to drop out somewhat.  "C", not in this sample, has the
     same problem.

   - "Qu" are set right up against each other, with insufficient
     whitespace between them.

   - "M" is distinctly asymmetric.

   - The enclosed loop of "a" looks muddy, as it is partially filled
     with grey.  Contrast with "a" drawn without the bytecode
     interpreter, which has a nice clear loop.

The font in use here is "QuickType II", copied over from my Windows
partition, where it was installed by I-have-no-idea-which-application.

Can somebody help me understand what I'm seeing here?  Why would the
bytecode interpreter make things worse?  Does this suggest that the
specific font being used just has uniquely bad bytecodes, or would this
effect appear for other fonts as well?

Thank you!