Hi
The Zoom effect does not work on a text image. (VP 8.45) This may be a programming constraint-deliberate omission or an oversight. (Even a bug :o) but once the rectangle is altered the text disappears.
Use Pan & Zoom instead but don't move the placement of the rectangle, just alter its size between start frame and end frame. Note that this effect (unlike Zoom) works on the whole image clip duration and keyframes cannot be used to stop the zoom before the end of the clip.
Nat