My Elbow is retarded

hello everyone,
I made lots of progres with api revit, but some times Revit api just loses me.

I made app that create pipes and put fittings. When i try to rotate elbow 180 degrees this what happens;

My steps are:
1)create pipes

2)made elbow with direction the same as pipe

3) the for some cases I made line from point of inserting elbow to elbow point + direction and rotate elbow 180 degre

4) then i move pipes to elbow connectors and connect it.

work almost evry time but for some case it made this(picture)

I can't use document.Create.NewElbowFitting() because it dosen't work for pipes that end in the same point.

what i would like to know is why sometimes revit deforms instance?