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