The cursor gets sticky when selecting an element in the user interface. It is extremely difficult to deselect an element after it was selected making editing work impossible. I checked for a solution to this problem in the forum but could not find it.
Please try with the actual Kdenlive AppImage version 18.08.2 Run the Appimage from the terminal (press CTRL + ALT + T). Move to the AppImage folder and run the .AppImage: ./Kdenlive*.AppImage
As it has been a while since this was reported, all the timeline code was rewritten to avoid exactly this kind of issue. Feel free to reopen this bug or create a new report if this is still happening with the latest version (https://kdenlive.org/en/download/)