From the manual on page 36
Set focus mode selector to S or C for autofocus operation.• Set focus mode selector to S (Single Servo AF with Focus-Priority) or C
(Continuous Servo AF with Release-Priority). Camera continues to focus
automatically on the subject when the shutter release button is lightly pressed.
S: Single Servo AF with Focus-Priority
The shutter can only be released when in focus indicator / appears in the
viewfinder (Focus-Priority). Once focused on a subject, keeping the shutter
release button lightly pressed locks focus (Focus Lock). With a subject that
has been moving, the camera continuously focuses on a subject as long as
the shutter release button is kept lightly pressed (Focus Tracking, page 68)
and focus locks when the subject stops moving.
C: Continuous Servo AF with Release-Priority
Since the priority is on shutter release, you can release the shutter
regardless of the focus status (Release-Priority). Focus is not locked when
/ appears in the viewfinder and the camera continues to focus on a
subject until shutter release. With a moving subject, the camera
continuously focuses on a subject as long as the shutter release button is
kept lightly pressed (Focus Tracking, page 68).
Then on 68
Focus TrackingWhen the focus mode selector is set to Single Servo AF (S) or Continuous Servo
AF (C) and the shutter release button is lightly pressed or AF Start button is kept
pressed, the camera automatically switches to Focus Tracking when a moving
subject is detected. Focus Tracking enables the camera to analyze the speed of
the moving subject according to the focus data detected, and to obtain correct
focus by anticipating the subject’s position—and driving the lens to that
position—at the exact moment of exposure.
In Single Servo AF, Focus Tracking is activated with a subject that has been
moving in advance to the focus detection, and focus is locked when the subject
stops moving and / appears in the viewfinder. In Continuous Servo AF, camera
continues to track subject (even with a subject which started moving in the
middle of the focus detection) and focus is not locked.
So what's biting me is the Focus Priority feature. It sounds like your issue is with the Focus Tracking. Looks like these are both unable to be adjusted like they can be on the newer DSLRs.