3dsmax - freeform modeling tools issue

Obscura

Currently I'm doing a retopo on a mesh, and I'm doing it with the freeform modeling tools, on the mesh's surface. Everything worked fine, and ever, until now. When I'm trying to place a new polygon, it deletes an existing one. I tried to start a new mesh. As a test I tried to place a small plane with a few segments, and then I've switch to the freeform polygon create, and tried to continue from that plane. Still the same happened, When I tried to place a new vert , it deleted an existing polygon from my plane.

Anyone ever met with this behaviour? How it went wrong? How could I repair it?