Missing file icons left of the download file names

[crazy-to-bike]

Hi,

I offer pdf files to download with Phoca Download. Left of the file names appears a pdf icon. See
https://www.crazy-to-bike.de/download/formulare.html

But I also offer gps files with filetype .gpx
In download configuration I added {gpx=application/gpx+xml} for allowed filetypes

In the Joomla directory /media/com_phocadownload/images/mime I added an icon named icon-gpx.png in the folders 16, 32, 48 and 64 with a size of 16x16, 32x32, 48x48 and 64x64 pixel.

The gpx files can be downloaded, but the gpx icon doesn't appear. See
https://www.crazy-to-bike.de/downloads- ... hweiz.html

Caches are cleanded.

Why doesn't the symbol for gpx files appear?