Yes, I assumed that
I think there is something wrong with the button itself. A colleque of mine has got an iLiad too and he told me that the zoom button on his pdf-viewer has a different appearance.
His symbol shows a little rectangle in conjunction with an arrow pointing to and surrounded by a bigger rectangle with a dotted border. On the other hand, the zoom button on my iLiad pdf-viewer shows a little dotted rectangle within a bigger full line bordered one.
As I stated this symbol is not hidden and clickable in pdf-mode but beside refreshing the display two times it does nothing do.