I've seen posts where it's said that there is no solution to this problem. I want to move vertices on my retopo mesh, with them being constrained to the original hi-poly model. They actually fly away in the outer space. Does anybody found a wayout to this?
Those are hard edges (or the vertices aren't welded). Try selecting those edges and going to Normals > Soften Edge. If that doesn't work, make sure you've combined both objects and welded the vertices right.
Still vertices were appearing and disappearing, seemingly on a whim, then I discovered that pressing my Maximize Viewport toggle shortcut, all vertices reappeared. :) Since then I'm using this fix coupled with above config.
so different vertex color means different material instances being applied to that specific vertices is it? If its twice as tall as it is wide, does that mean i can make it vertically beyond 0-1?
Do you mean you can't see your vertices while in the edge sub-object mode, or that you can't see any vertices at all? :O I don't quite get the question.
Have you made sure that all the vertices along those edges are welded, and/or if there are any double-edges/thin faces in there? To me it looks like those sharp waves are made by non welded vertices.