[MicroStation V8i SS4] Bing maps incorrect rotation after applying helmert transformation

Using MicroStation v8i SS4 08.11.09.829.

I have a DGN file with a GCS in it. I am using a Helmert transformation to define a rotation of -4.7641666 degrees and a scale of 1:500000. The Helmert transformation parameters therefore become:

Helmert A: scale times cos (rotation) = 500000 * cos (-4.7641666) = 498272,4987

Helmert B: scale times sin (rotation) = 500000 * sin (-4.7641666) = -41527,3048

When I attach a Bing Maps layer, the scale looks about correct but the scale doesn't. The rotation is Bing Maps is about  206 degrees (rough estimate).

When using auxiliary coordinates or exporting a KMZ to Google Maps the result is correct.

If I set the rotation to 0 degrees (and therefore Helmert A to 500000 and Helmert B to 0), the Bing Maps raster is correct.

I have a sample DGN if necessary.