The configuration scanner doesn't treat spaces and tabs equivalently
in php3.ini when using keywords (as opposed to numerics, which do
work).

Here's the php3.ini in question:

[PHP_3]
; T == tab; S == space
track_vars      =       On      ; (T/T/T) works
;track_vars     =       On      ; (T/T/S) doesn't work
;track_vars     =       On      ; (T/S/T) doesn't work
;track_vars      =      On      ; (S/T/T) works
;track_vars      =       On     ; (S/S/T) doesn't work