So the file that's saved does not have the name you gave it in the export dialog?
That would
seem to be impossible. If you type in "XYZ.WAV", SONAR will use
that file name, verbatim, assuming you've also chosen "Wave" as the file type.
Even if the selected file type is incorrect, SONAR will use the file extension you entered and switch to the appropriate format. For example, if you intentionally select w64 as the file type, but enter "XYZ.WAV" in the file name textbox, SONAR will automatically change the type selection to "Wave". It does this so that the file extension always indicates the actual file format.
Here's a thought...are you sure that the .w64 file you're looking at is actually the one you just created? By that, I mean if you manually delete it before re-exporting, is the .w64 file then re-created? I have inadvertently exported files to the wrong folder before, and was then surprised when I listened to the exported file that it was an older version.