Bouncing text?

[Chip Salzenberg]

The baseline of text seems to bounce up and down when switching
to/from the fixed font (@F).  I'd expect "this @F{and} that" to share
a common baseline (the bottoms of the letters without descenders).
But it doesn't.

Any hints on how to make the baselines line up?
-- 
Chip Salzenberg      - a.k.a. -      <address@hidden>
      "When do you work?"   "Whenever I'm not busy."