It will This will happen if you have more than one editor pointing to the same project (you or your colleegue). This is the reason why there is a locking mechanism, but that mechanism still allows you to overrule the lock.
Also, suppose you have a project open in an editor, and then you get a phonecall or otherwise distracted, and when you get back you open a new editor. You work in it and all is fine. Then you encounter the old editor and close it. It might overwite your work with the older version.
We're trying to prevent this from happening, but we don't know all the scenario's.
Also depends on the version of xerte. Could multiple instances of the editor be a cause in your case?