Cannot save item in custom list

I have a strange issue.

I duplicated a web application to our QA server from a production server. All existing sub sites and lists seems work fine. However, when I created a new sub site, I have problem to save item in any custom list.

1. The "save" works on document library.

2. If I add a new item via the new item form, nothing happen when I click the "save" icon/button. The list only contains the default "Title" column.

3. If I add a new item via the list form "Edit this list", I am able to add and save items. That means this is not a permission issue.

I appreciate any help. Many thanks