I have experienced this problem in the past. It first started when the clipboard history feature was added. For me, it seemed to be an interaction with a system-wide clipboard history program that I already use. Since I have that program already, I turned off the built-in one and the problem went away.
I tried turning it back on and it still works okay, so there must be some other factor as well, but I would definitely look at what other programs/utilities are running that interact with the clipboard.
I have also seen that same delay/lag happen in MS Excel on another computer that doesn't even have plsqldev installed. It does have the same system-wide clipboard history program. On that system, the delay in excel goes away when closing the clipboard history program.