Okay, now I know what's going on I can explain it properly, though it will take a bit of explaining:
A clip in my project has a sudden change of scene. I'd like to change this to a cross-dissolve. I cut the clip at the scene-change (using the Blade), and then put in a cross-dissolve with Cmd-T.
What happens? Well, it does exactly what it's supposed to, but it appears not to, since the sections immediately before and after the Blade are blending with exact copies of themselves.
(I can see the grey rectangle which indicates a cross-dissolve but when I play it I just see the same crude jump from one scene to another.)
Now, in 10.0.1 I could instruct Cmd-T to force an overlap to get the effect I want to. (It was an option in the Preferences). But I can't do this in later versions.
So how do I do it? One way is to turn every single clip into a Compound Clip. By doing so, it has no handles, so when I make it cross-dissolve it will shorten my project and produce the ('true') cross-dissolve effect I want. But this means clicking on each clip individually and making it a Compound, and since I need to do this about fifty times in my project, it's a bit tedious. So is there a quicker way?
Thanks, and sorry for the previous mis-post.
MST