Yes, Carrara Studio 2 and 3 have what I like to call Vertex Float problems. You place a vertex right where you want it (ex: 1.00,2.05,1.00), and frequently Carrara decides it wants the vertex somewhere else (ex: 1.00,1.04,0.99). I have not done any modeling in Carrara 4 yet, so the problem may still be there...or not.