The following steps lead to a confusing misbehaviour of Qt Creator's File System view:

• open a File System view inside Qt Creator
• create a new file externally in the directory shown by the view (the file wont't be visible from inside Qt Creator at once. (That is because the view doesn't update peridicaly, and is no bug so far).
• switch to the parent directory and back again (now the new file is visible)
• open any other file but the newly created by double clicking on it (the new file is not visible anymore)