Can you post some screenshots or an animated gif to illustrate the behaviour?

I absolutely dont know how to do gif...  

Can't really understand the issue for one screehshot. But... Green dots are vertices (corners). Drag Blue dots to add another vertex. Double click on a dot to delete it. To find software to do animated gifs, just google "open source animated gif". For example [https://www.screentogif.com/](https://www.screentogif.com/) Or, install something that allows you to creae video screencapture for free then upload the video to one of the free online video to animated gif converter sites such as [https://ezgif.com/video-to-gif](https://ezgif.com/video-to-gif).

lower rignt node does not move when I left click on it. That's all... I just want to move it to make the angle 90°... I can move the other nodes of the shape. I can make right click and "delete node" box comes. I've deleted about 20 times on that node without effect.

I'm a noob... I closed all and re-open ... it's ok sorry for  trouble.