Using WCS layer in QGIS for processing gives FAILURE: Missing destination

I have a GeoServer serving raster dem data out via WCS and can add the layer easily to QGIS (3.2) but when I try to use it as the input for an operation (e.g. HillShade) I get an error.

Processing algorithm…
Algorithm 'Hillshade' starting…
Input parameters:
{ 'ALTITUDE' : 45, 'AZIMUTH' : 315, 'BAND' : 1, 'COMBINED' : False, 'COMPUTE_EDGES' : False, 'INPUT' : 'dpiMode=7&identifier=training:panorama&url=http://localhost:8080/geoserver/ows?version%3D1.1.1', 'MULTIDIRECTIONAL' : False, 'OPTIONS' : '', 'OUTPUT' : 'C:/Users/ishare/AppData/Local/Temp/2/processing_868cc25180f24d9f8e193bc0cfedb6d3/7cf48f64d8b54ee694c3ee93ed17e903/OUTPUT.tif', 'SCALE' : 1, 'ZEVENBERGEN' : False, 'Z_FACTOR' : 5 }

GDAL command:
gdaldem hillshade dpiMode=7&identifier=training:panorama&url=http://localhost:8080/geoserver/ows?version%3D1.1.1 C:/Users/ishare/AppData/Local/Temp/2/processing_868cc25180f24d9f8e193bc0cfedb6d3/7cf48f64d8b54ee694c3ee93ed17e903/OUTPUT.tif -of GTiff -b 1 -z 5.0 -s 1.0 -az 315.0 -alt 45.0
GDAL command output:


FAILURE: Missing destination.

Clearly the missing destination is a red herring, and it is failing to understand the WCS layer as an input. But GDAL is built with WCS support included so shouldn’t this work?

Do I need to do something else or start working out where to hack the QGIS code?