Cannot click OK after searching for runtimes

I stumbled upon this problem while testing JBDS 4 on RHEL6, but I don't think it will behave differently on RHEL5 or possibly any other platform. In fact, I just confirmed that the same happens on Mac.

In JBoss Tools preferences, when you add a new path for runtime detection for the first time, it find everything, but the button OK is not clickable. If you check and uncheck the checkbox next to the found runtime, then you can click OK with no problem.