Ah, after adding some more tests I recall the fundamental problem... inkscape:document-units doesn't allow for arbitrary ratios between width/height and the viewBox. I wonder how easy it would be to fix this. If it is not fixed, the files with mixed units created with 0.91 will have problems in 0.92. (One should be able to created files with arbitrary ratios.)
Ah, after adding some more tests I recall the fundamental problem... inkscape: document- units doesn't allow for arbitrary ratios between width/height and the viewBox. I wonder how easy it would be to fix this. If it is not fixed, the files with mixed units created with 0.91 will have problems in 0.92. (One should be able to created files with arbitrary ratios.)