fd.filefilter not persistent?

Hi! I'm trying to use the FileDialog to allow the user to select a sound file, thus:

Dim fd As FileDialog
fd.FastScroll=True
fd.FilePath=BestFileLocation
fd.FileFilter = ".aac,.flac,.m4a,.mp3,.ogg,.wav,.wma"
TmpI=fd.Show("Choose Sound","Ok","Cancel","",Null)
If TmpI=DialogResponse.POSITIVE Then
.
.

I find that if the user chooses the ".." from the dialog box (going up a directory level), and maybe navigates down to another directory, suddenly the filter parameters are ignored.

Is there a different way to filter which files are shown, so that only files of xxx type are listed regardless of where the user navigates?

As always, thanks!

DTs