Bonita runs 2 instances of tomcat

When I try to run a diagram after quitting Bonita, a dialog box with a progress bar and a description of "First run, waiting for engine to start" appears. That progress bar will never finish loading, until it got interrupted by an error message saying that Tomcat is already running, after the default timeout of 300ms. Checking the netstat will show that there is a double usage of port 8080 and 8009 by the same process ID. It will not happen unless I run Bonita, which means that Bonita is running 2 instances of Tomcat and thinks that its process got blocked by another instance of a Bonita Studio or something else.