I also just checked the new version, the rendering of V3 maps with V4 themes is wrong.
What renderer is used for V3 maps with V4+ themes? If it's the forked 0.3 version (locus-extended) it makes not a lot of sense, as at least mapsforge 0.5+ is needed.
I would propose checking the theme version in the xml-file, if it's version="1" and/or locus-extended="1", use the Locus-Fork, if it's version="4" or higher, use the standard engine.