The Type column in Explorer is determined by inspecting the file extension not the contents of the file. It is easy for SONAR to export a file with .5 as the extension by added the extension when naming the file. For example, if I use test.5 as the file name in the export dialog an audio file called test.5 will be created. It will show a type of 5 File but will be the format specified in the export dialog.

jatoth...........yes......the name of the project is "0.1 + 0.5".

And you don't have any of the above mentioned software installed?? 
Does this happen to all projects? Have you tried a different project?
So for sure the export dialog is set to WAV but it gets changed somehow??  
What happens if you choose MP3? 

scook.........I'm going to change the project name and see if that helps.

The file being created is just what you named it. The part past the final . is the file extension. In this case a 5. This is why Explorer is calling the file a 5 Type. Do not use dots in your file names if you want SONAR to automatically add the file type extension. If you are going to add dots in your names add the extension to the file name entry field.

OK, the project name was the problem and I changed it. [project name was: 0.1 + 0.5].  Just to experiment, I tried to import the 5 file. Import will only recognize the wav file in the folder. 
 
Thanks for responding everyone. You're all champions.