It would appear that the "Ruby class directories" configuration for flog is tab or newline separated. (I had to check the source code to find out.) Neither of these separators are easily/conveniently added in the web form when configuring via the gui (although a copy/paste will work in a pinch).

I would recommend either 1) changing the web config form field so that users can "Click to expand multiple lines" (as is the case when using the "Invoke Rake" build steps), 2) modifying the separators to include colon or comma, or 3) at the very least adding which separators are supported into the help text (so that the next person won't have to consult the source code).