Not all effects in the G-Force are full stereo, several effects actually create a stereo effect from a mono input.
Mixed left/right or left only input
When mono input effects are routed directly after the Input section they'll mix the right and left signal halves together (Ralf found this), but when routed after another effect block all except the Panner mute the right side of the stereo signal, thus only allowing the left stereo side to enter.
This means that if you pan a Panner, Delay or Pitch Shift signal hard right the panned signal becomes muted if a mono input effect with 100% Mix is routed after it. The reason for this, according to TC Electronic, is that an Advanced Chorus/Flanger with Phase Reverse On would otherwise be cancelled if its phase reversed stereo output was mixed together by a following effect block. Despite this the Panner input still mixes the left and right stereo sides together for some reason.
The Filter block is stereo in and out except for the Phaser, which is left only in and (very subtle) stereo out.
In the Panner/Tremolo block the Tremolo is stereo in and out, while the Panner is mono in (left and right mixed), stereo out.
The Pitch Shift block is left only in, stereo out.
In the Delay block, the One- and Quad tap delays are left only in, stereo out. The Stereo, Dual and Dual Two tap delays are stereo in and out (the Dual Two tap giving you two taps on each stereo input side).