Hi,

It is due to difference in installed modules in both instance, initially in the sales module, the order line field is set as editable bottom, and the same has been inherited in some another module and removed the editable bottom option, so once you click add an item, it will open a pop up, ie, form to edit and save.

Here what you can do is that, go to apps menu, and make sure same modules are installed in both the database. if you install same modules in both the database, you will get the same functionality in both the database. I am not exactly remembering in which module it has been inherited and changed. I think you can make a quick look at the apps menu and find that module.

If the above is not the case, make sure the sale order records is in draft state, so that you can edit also same settings for the sales in configuration.

Thanks