I can see there is not exactly lively debate about this issue on the web site, so I will add a little more from my experience a month an ago and hope that it can help others.
The edit cursor is defiantly a weird problem, going from a normal light blue vertical line, meaning it works, to a 1/4" horizontal black line with 2 arrows, where editing is not possible.
Every time I opened the Sound Editor, I tried new things, like clicking in different areas in the editor or opening a menu and selecting something before editing, nothing seemed to have an impact.
Then moved the mouse into the edit area and the double clicked or triple clicked the left hand mouse button while being in the edit area. It was (is) important not to move the mouse at all while clicking the mouse and to do it rapidly.
Here is the weird part, after that, the light blue vertical line edit cursor has worked ever time sins (for weeks, without the need rapid mouse clicks first).
That almost sounds like "self-healing" software - not a big fan of that theory. The question could also be, did other software have an influence? Like Norton's Security? Or could it be a weak programming area, where timing is critical. That still stands as an open question. Hope this will help somebody else, which falls into my dilemma. And of course if you have a different way to solve the problem, please expand and tell us.