Desk top version, seems to work, if I understand correctly. What I did...
> on page one created a shape and entered some text.
> on page two created two shapes to try two differrent techniques...
1) first shape,
> added User Section, entered formula: =SHAPETEXT(Pages[Page-1]!Sheet.1!TheText)
> then, for the shape, Insert > field > User Defined and selected desired row
2) second shape, directly used the Insert > Field > Custom Formula = =SHAPETEXT(Pages[Page-1]!Sheet.1!TheText)
Now, back to shape on page 1. Select and type new text. Works fine. Both shapes on page 2 update immediately.
Other than that this was on a desktop PC, is your process different?