Some keyboard enhancer or malware/keylogger. Be sure it's not malware with Grif's list of scans at http://www.cnet.com/forums/discussions/how-to-remove-pup-option-603542/#post-f742c795-5881-433b-a29b-6d758efe5cd3
It also could be user error but the only way to find that is to watch the user and video the typing so you can show them the error.
Two of my computers -- a Win7 machine and an XP SP3 machine -- often change the positions of typed characters, especially spaces and periods, when I'm entering text on a webpage or in the URL bar of Firefox. Thus I get, for example, "ww.wfacebookc.om," when the URL was typed correctly. Or on the youtube search bar, I might get something like "ElvisP ressley."The problem does not seem to occur with MS Word, Excel, etc. One keyboard is Microsoft, and the other is HP. Replacing the keyboaard does not seem to make much difference; at least not for long. All suggestions appreciated!