My user account has disappeared from a computer with ubuntu server 12.04. I discovered this by trying to ssh to it, and the owner of this machine confirmed that my user was gone by attempting to "su user" (my home folder was still there, though, with all it's files). The account was recently set using terminal commands and the only thing that happened (that I could identify as probable cause) between then and now was that the computer was turned off and on. The owner of the computer also complained of trying to change his password only to have it reset itself back to the previous one (I wasn't told if this happened immediately or also after restarting the machine).
Any idea on what is happening? Is it possible that some routine is overwriting the files where user information is stored when the computer starts?