Hey, thanks for bringing that to my attention. The issue only seems to occur while you're logged in though.
As a workaround you can open the affected forum section in a private browsing window (Ctrl + Shift + P in most browsers, Ctrl + Shift + n in Chrome) and copy the topic into the browser window where you're logged into the forum.
There are two minor releases that our installed version of Kunena is lagging behind. I'll update the software next week. Hopefully that will will fix the issue.
- seb