I just did the maneuver you described several times in Imported Items, and no freezing.
I suggest upgrading to Adobe 10 Reader, since I had multiple crashes and quirky behavior in Imported Items with Reader 9. If you already have Reader 10, then a work-around is to right click on the imported item that you wish to enlarge, and choose "Open (in Default Application)", which will open the document outside of the Amazing Charts window.
