Hello all,
I am running git version 0.15-1510-g92de0f3.
When i tell Tania to follow me after i free her then turn on invisible mode, she
follows me, but not directly.
She stands in the same spot until i reach the desert surface, where she stands
on top of the "ladder" until i reach town. When we get to town she walks inside
of the entrance like normal.
The most queer thing is that no matter how fast i run to town, she always
appears when i step into the town.

Hope this helps. ;)

-Sydney (IRC head8debian)

Discussed in IRC
User noticed in "god mode" will attempt to replicate locally.

I can confirm OP's original observation.
Using cheat modes: Invisible: ON; god mode: ON

With Tux invisible, Tania will respond to the dialog prompts to initiate her
escape and return to town.
Underground, she does not follow Tux.
Upon reaching the surface, Tania suddenly appears next Tux but will not follow
Tux into the desert.
At the town gate, Pendragon will stop Tux and proceed with the dialog as per
normal. On exiting the dialog, Tania is suddenly present next to Tux.

PoA (plan of attack)
Alter Tania dialog: Disable "follow me to surface" in underground portion of
dialog if Tux.is_invisible().
Should also have an event trigger if Tux gets too far away from Tania to prevent
Tania suddenly "appearing".