I am processing raster data for Austria in EPSG:31287 (MGI /Austria Lambert) and all input data as well as the project itself have this CRS properly defined. When I run different raster tools from the GRASS toolbox in QGIS (I used Version 3.12 and 3.14) (in my case r.reclass and r.neighbors) the CRS of the output file gets a user defined CRS named USER:100029 plus a lot of projection parameters (those parameters are ident to MGI /Austria Lambert specifications plus WGS84 to MGI transformation parameters). The raster cells of this layers are visually slightly shifted in the map view (see images below, the raster cells are 10x10m).

When I change the CRS in the layer properties > source to EPSG:31287 or assign EPSG:31287 as projection (with GDAL > Raster projections > Assign projection) everything is fine. The thing I want to understand this issue and search a for a solution to avoid the additional this projection assignment. Furthermore, I am teaching GIS, and the rookie students a really confused with problems like that...

Is this a bug, or can this be fixed somehow?

The USER-CRS in the layer properties

Left: The visual shift of the yellow raster cells caused by the USER-CRS; Right: The same raster with the assigned and without this shift

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