I have the "Single Click on a plugin to open its GUI Window" option set. Initially when adding a plugin, single clicking the filter block does not open the GUI. You have to either double click, or click elsewhere then click the filter block again.*
Here is an image of it in action (note that you can see the mouseclicks with a small circle around the cursor as they occur).

* I don't think "filter block" is the right term, but hopefully you get what I mean.
