By default, Zotero will try to clean up casing/capitalization of item titles when items are imported (e.g., titles in ALL CAPS will be converted Title Case). To disable this function, follow these steps:
1) In the Advanced pane of Zotero preferences, on the “General” tab, click the “Config Editor” button.
2) Find “extensions.zotero.capitalizeTitles” in the list. To find it quickly, you can type “capitalize” in the Filter box.
3) Double-click “extensions.zotero.capitalizeTitles” to toggle between the true and false setting.