Mysterious lines of code being added to my website

[bellaisblue]

A client contacted me with a small edit for their website. Once I fixed the page (just had to edit a phone number) and re-uploaded it to make it live, I noticed that some random letters were added to the bottom of the page.

I thought that was odd, so I uploaded the page again, but they still appeared. So I downloaded the page from the server, and sure enough, a few extra lines of code had "mysteriously" been added to the bottom of the page. It was like it took the last 5 lines of code that I had written, and duplicated them. So I removed them, re-uploaded the page, but they returned.

I then noticed that this was happening on some other pages as well, which also happen to be the most recently updated pages.

I keep doing the most obvious thing of re-downloading the pages from the
server. Removing those extra letters. Reuploading the pages... but then they appear again.

I use COREFTP to upload because it needs to be SSH. Port 22 (if that
matters).

This is strangest FTP experience I have ever had.

Do you think:
1 - This is a problem with the FTP software?
2 - A problem with the way I am connecting to the server?
3 - A problem with the server?
4 - Something else?

Help would be greatly appreciated.
I'm dumbfounded.
--BB.