The Kunena team has announce the arrival of Kunena 7.0.4 [K 7.0.4] in stable which is now available for download as a native Joomla extension for J! 5.4.x/6.0.x. This version addresses most of the issues that were discovered in K 6.2 / K 6.3 / K 6.4 and issues discovered during the last development stages of K 7.0
I think that we can honestly say that Kunena 1.0.10 exposes a number of Javascript vulnerabilities, especially if you are using Community Builder. Are you using Community Builder, Keith? Did you upgrade to K 1.0.10? The upgrade may have caused the problem you've just reported.
I have successfully deleted messages on my K 1.0.10 site and not encountered the Javascript symptoms you're referring to. I never experienced these problems with K 1.0.9.
Probably doesn't matter. Either your current Joomla template or some other published extension is causing the Jscript conflict. I'd start looking at one of the JS ones in your case.