Fixed with a new User Profile.

OK - here we are in 2019 and I'm trying to copy and paste Markers from one Master clip to another (MC 2018.12.6, Mac OS 10.12.6). It just will not work at all. I've tried with Avid media, linked media, clips with identical duration and timecodes etc. If I export as either text or XML and try to reimport, I get a warning that the Record monitor

Shift+Cmd+W (look in the File menu).

Install plugin and link.

Select clip - hit Return (I'm sure this has been mentioned).

All good here. Mac OS 10.13.6.

And (on squinting at the new UI), the button to toggle transition effect adjustment is right there in the Timeline Toolbar. With the very limited highlight colours in this version it is very difficult to tell which button is highlighted.

Source Settings> Reformat?

Right click here (there should be an image)

The Smart Segment and Trim Tools are accessed by a right-click. Transition effect adjustment seems to be on by default. Make sure you create entirely new user settings and also trash the old site setting file or you may not see the correct UI.