AutoCAD 2013 :: Polyline Turns Into Lwpolyline?

We use only polyline when drawing. Plinetype is set to 0.

First problem is with J (join) command. Sometimes when we try to join different polylines it kills a vertex. Example if i have two polylines (they are not joined) that forms a rectangle it will join them but kill one vertex and turn it into triangle. This dosen't happen all the time.

Second problem i figured a way round for the problem above, if i use the pedit command and then use j the above problem never happens. But instead (also not every time) it turns the joined polyline into lwpolyline. So its all pretty anoing as we have to use convertoply.

Is there some other command than plinetype to resolve his problem.