All Macs are using the same version of ID (6.0.6), same operating system 10.5.8, same version of Helvetica, but on one Mac we are seeing text reflow - am I missing something really obvious somewhere? I've checked through the preferences but nothing is jumping out at me. Any ideas??
The most likely cause is a difference in the fonts installed. If it were a common font family like Times Roman, for example, you may have different versions of Times on that computer.