Client has reported this issue on several iMacs (10.7.2) running Illustrator CS5.5 with Suitcae Fusion 3 containing a clean font library.
Designer can be working with text (on a greeting card design) and the font they are using (live and active in SF3) will suddenly change to Myriad Pro.
If the user performs apple-z, the font will switch back, therefore presuming it is a keyboard command (clashing or remapped?) as they cannot associate
the change with any menu procedure.