please open the attached file: it is a simple default scene with cube animated in straight line from 0 to 100
I enabled motion path Around frame. it should display 40 frames before, and 40 after.
but it stops at 50 .
go to In Range tab,
scrub the End value to 20.
Click Calculate Path, it does not update…
workaround is to Clear Paths, then recalculate path
now set End to 100. Clear path, recalculate path.
Go back to Around frame tab.
Now the initial problem is kind of fixed…

I understand the path calculation in not interactive (depsgraph?) but I do not think you first need to clear path, to recalculate…

also Around Frame and In Range are to separate tab, that look supposedly independent….

furthermore you can see the green square (keyframe at frame 50) is misplaced, plus it blinks when you scrub frames

sorry if this is a bit messy, it just shows some problems with motion paths

tested on trunk r43948 , release 2.61 , mac and windows