Bug : uploaded folder not uploaded in the correct folder

Something strange just happened on build 2157:
1. Download a folder from FTP to my computer
2. Rename the folder on ftp to "xxx_old"
3. I modified files on my computer (without renaming files names
4. Upload the folder with modified files from my computer to FTP
The xxx folder i just uploaded is not containing all files.
Missing files were uploded to the "xxx_old" folder erasing old files without prompt!
I think it's a quite critical bug

I'm unable to reproduce the problem you have described.
Could you be more specific of what you are doing? The best would be a video which shows the exact steps. For example with camtasia or http://www.screencast-o-matic.com/
Thank you.