Sorry but I still able to see this rectangle using 3.1.3 GA. Try to clean caches.
And if this will not help - please show more code and info about environment.
Here is demo web application http://www.szymanski.pronet.lublin.pl/pliki/demo.war with this problem.
Apache Tomcat 6.0.14
Apache MyFaces 1.1.5
When I repleace RF 3.1.3.GA with RF 3.1.2.GA, dash-bordered rectangle is being displayed.
I do have the same problem after upgrading to 3.1.3. Cache is not causing this problem.
Would be if you could find the soure of that problem, will have a look into the project as well.