"paste and clipboard" in messages app

Ok, yeah I'm seeing the bug.
There's a workaround that works for me, worth a try. Tap the quick reply box, start typing (it won't work), tap again in the box and then try typing again.

If this doesn't work you can select 'Reply' (without quote) for any new post.
 
I have the same thing, using Messages with Gboard, if you delete all the content in clipboard it goes away, but will reappear once you copy something.