I use Zotero on Mac and also two Windows 7 machines. On Windows 7 machines, when I attempt to manually add a new item using the "+" tool, almost all field boxes are missing, although their titles are there. Some have just a sliver of a field and I can click on these and open the entry box. But all this works fine on Mac...all field entry boxes visible and working.

However, all three machines sync very well.