The same major symmetry bug can be observed by also following these steps:
1) Create a symmetrical voxel model
2) Right click on voxel layer in tree and select "Auto retopology"
3) Leave all fields unchanged except "Approximate Polycount", changing this field to 400
4) Click through the following dialogs without adding density shading or guidelines
5) When whole mesh appears in Retopo Room, select "Merge for per-pixel painting with normal map" - (an incredibly long menu option)
6) When dialog appears, don't change default settings
7) Observe 1/2 model in Paint Room.
I see the same phenomen in the last couple of Builts (including the Release-Candidate) also with leaving all Values at Default.
Edit: The Retopo-Mesh gets created entirely but only half of it gets merged.