Joining points not working

I am not completely sure if this is a bug or not - Create a line - Create another line (see screensshot ) - Select both and choose path combine - When selected , choose converted selected object strokes to paths , we want to make an unified path - Insert new points on both the paths (shown on screesnhot , red rectangle) - They refuse to join by either join selected nodes , or join selected endnodes with new segment ( shown on screenshot ) - The cusp nodes snap together, but refuse to be permanently joined  

issue