I have created a Webform, which has two file fields (i.e. Attach document 1 and Attach document 2). Both of them are mandatory and files are to be uploaded in the "Private" folder.
Now when someone attaches the files and submits the form, it throws error messages "Attach document 1 field is required" and "Attach document 2 field is required". If I invoke the validation, then it works. I have checked in the server and the files are uploaded properly. So I think it is "Webform" or "Form" issue.