Trying to copy a run of text (more than one line) from the Script Editor seems not to work because the clipboard is not changed and contains outdated data.
Selecting just a single line and copying it works.
Cut removes the selected text but a subsequent paste is not possible.
This hit me too. I pasted a short script into the SE and each line almost was flagged as an error.
I had to retype each line. Editing the line wouldn’t fix the error flag.
There was no visible difference between the flagged line and the acceptable line that I could see.
Quite bizarre.
This issue should be fixed in the latest version out now! Give it a try 