Text editing using AE under Android

Hi,
I have create a text box containing  this words  Prezentation  Agenda
I tried to correct the typo error  but when  I put the curson on  z
I obtained  Prezentation  AgendaAgenda and more ,,

Prezentation  AgendaAgenda Prezentation  AgendaAgenda 

What can I do to edit the TEXT ? 
thanks carlo