Thanks for the reply.
What you describe is similar but possibly not quite the same. Here is what I did:
I have a midi track consisting of several sections.
I double-click one section to open the midi editor.
I select a group of notes and then click Copy.
I then scroll to another part of the same midi section.
Move the playhead to where I want to paste the notes and click paste.
Instead of the midi notes I copied being pasted into the section, nothing appears to happen.
When I go back to look at the track view 2 unrelated sections have been pasted at the end of my song on more than one track!
It is possible that these 2 sections were ones I had copied previously but they appear at the end of the tracks and not where I had the playhead to paste the midi notes.
This has happened several times but not every time, so it makes it difficult to reproduce to order.