When pasting text with a link to an internal resource, the manager url is prepended to the link tag. For example if the link in the copied text was [[~123]], it becomes /manager/[[~123]] when pasted.
Update: Upon further investigation, this happens in Chrome (78.0.3904.87) but not in Safari. I’ve not tested Firefox or Edge/IE yet.
I’d like to bring this thread back to life because it’s happening to me too.
When copy/pasting a normal link in the text editor, like: my-cool-cat
the full URL and manager directory is being added to the url, like: catsite.com/manager/my-cool-cat
rending the link useless.