When saving the database with the shortcut Cmd+s in OS X, the result depends on which field happens to be active in the JabRef editor (tested on both 2.7.2 and 2.8). The author field (and most other fields) are not changed, but the title field may change. The program seems to add an s to the end of the title, unless the title already ends with an s. This messes up the bibtex database somewhat... In contrast, one can use cmd+alt+s without any problems, but this is not a very natural keyboard shortcut.
I'm running OS X 10.6.8 with one of those small Apple keyboards.