For me, this is a recurring bug in 1Password Version 4.1.3 (413002)
When I first start 1Password, I can copy fields to the clipboard and paste elsewhere. After awhile, however, the copy button isn't available -- I can click all over the fields: no copy button, nothing copied to the clipboard.
If I quit 1Password, then restart, the copy button reappears -- then, after some indeterminate amount of time, I can't copy login IDs, passwords, nothing. I have noticed, though, that while I can't copy URLs, if I click on them a browser window launches.
This used to be my most frequently used feature -- until it stopped working.
Now it's just a growing source of frustration.
I'm running 1Password on a MacPro with 10.9.1
Please FIX this bug!