I use Koi 1.1.8 from Themify (free version) and I can only edit Links in posts when Events manager is disabled.
Event Articles work okay.
Where does EM interfere with regards to Liink Button that it could possibly not pop pup ?
I disabled all Plugins and only with EM it does the issue.
my last successful Post (on that website) was from 24.05.2012 (yes, not very active there ;-))
Any hint is welcome. I will also check some approaches taken by a similar issue with WP 3.1, but that was a year ago....