P.S. I upgraded WP8 to WP8.1 a week ago. So I guess it was a windows bug after all.

Phenomenon that text shrinks with zoom in no longer occurs.   Close this ticket.  Thanks.

Maybe its a windows bug?

Phenomenon occurs in both hybrid 13" laptop/tablet Sony Duo 13 Windows 8.1 and Lumia 1020 w/ Windows Phone 8.