All programs using the standard Windows file dialog boxes do this. In fact, the default extension is added by Windows, not NoteTab. If the extension you are using is is associated to a program or is listed in the dialog’s file-type list, then the default extension is not added. You can add any extension to the list by opening the Options dialog box and then activating the File Filters tab. Another method to avoid appending the default extension is to enclose the file name in double quotes (for example: "MyFile.2012").
Microsoft added this behavior with the introduction of long file names. You can now have file names like the following:
MyFile.2012.txt
The .2012 is not considered as being part of the extension. And if you type MyFile.2012 in the File dialog box and .2012 is not listed as a file extension (or associated with another application), then Windows assumes it is part of the file name and name does not have an extension – hence it adds the default extension.