fileout geotiff doesn't work for NCEP dataset

On our testbed-12 project we are unable to generate geotiff files from the underlying dataset:

http://testbed-12.opendap.org:8080/opendap/testbed-12/ncep/Global_0p25deg_best_hs002.nc.tiff?u-component_of_wind_isobaric[0][0][][]

And that seems to kill the beslistener.

Update 2019-02-25: We will have data on test.opendap.org in a 'ncep' directory that can be used to test this.