You are misinterpreting what it says. It doesn't say "Ti leading types always use Ti and always ignore Te", it says that Ti leading types "have very little use of Te". And even that is an exaggeration, IMO.
From The Dual Nature of Man:
Each individual has all eight IM elements contained in his psyche. In other words, each of us utilizes the same ways of receiving and processing information. However, in difficult situations that demand our intellectual efforts, people tend to rely on only one pair of elements — one black and one white. These are what define one's IM type.
In fact it's pretty hard for anyone to use
without using
. There's always a little bit of "spillover" between intro/extro forms.