Basically... you just need to copy some text. Even a single word is usually enough. And paste in the quick reply box below to check. I could replicate the issue in Chrome Canary and Dev. I am not sure if this has reached Beta. There is no delay in Chrome Stable.
The delay only occurs on the first paste. If you paste something again, it is pasted instantly.
Any suggestions on where to report it? XenForo or Chrome? I have filed a bug report on Chromium project but not sure if it is going to get any attention there. Cheers.