The confusion here is that FTP is not a program, nor is SFTP. It is a way to transfer files and can be used in many different ways.
You can use FTP/SFTP in a third party program, you can use it in windows explorer, you can use in our applet, etc. So if you can be more specific is HOW you are using FTP/SFTP then I can help you with your problem.
I assume you are talking about FTP/SFTP applet, but I could be wrong. I did test our SFTP applet just incase, but I was able to upload multiple files in multiple web browsers/platforms without any problems.
Without knowing what you are doing/what program/what version you are using, I can't offer any real help.