Uploading a revised version of a file doesn't work properly

I'm having trouble with different versions of the same file; after changing a file and uploading it again, I keep seeing the same file. I even ran this experiment. I upload the revised file and let pbwiki rename it with a -1 appended to the name. I then looked at each file from the list and they were different as they should be. I then deleted the original one and renamed the new one to the old name. Now when I looked at the new file renamed using the original filename, I was again looking at the old file. There must be some buffering going on. This has happened before. The only way to get around it seems to be to let it append the -1 on the file name and then change the link to look at this revised filename. Anything else doesn't work. (incidentally, I knew the old file from the new because the old file had some colored text and the new one has all black text). Any thoughts?