By default when Tomcat starts it creates 25 threads which listen for incoming requests. This is fine in a production environment but in a development environment probably only one or two threads are being used. When the server has a debugger attached and those extra threads can become a nuisance causing unnecessary scrolling to get a look at the call stack. Fixing the problem is simple:

Open the relevant server.xml file in the for the Tomcat instance you want to "fix". You will find them all under the Servers meta-project. Find the connector definition (which will look something like the one below) and change minSpareThreads to a low value such as 5.

<Connector acceptCount="100" connectionTimeout="20000" disableUploadTimeout="true" enableLookups="false" maxHttpHeaderSize="8192" maxSpareThreads="75" maxThreads="150" minSpareThreads="5" port="8080" redirectPort="8443"/>