extruding

I have, on a few occasions, successfully extruded lines into quads and quads into Hexes, but it seems once the operation is done for the first time, Salome loses sight of the mesh, even though it is visible on the screen. Therefore picking other elements on the screen for further extrusion becomes impossible. Does anyone know how to cirvumvent this problem?

Another problem I have is that Salome does not allow me to build models from Node upwards, always demandind an existing mesh be cited before a node is created. Is there a way around this?