The issue is caused by fixing JBIDE-12448.
When starting JBoss Tools the first time, you will get the following exception:

!MESSAGE An internal error occurred during: "Searching runtimes...".
!STACK 0
java.lang.NullPointerException
at org.jboss.tools.runtime.ui.RuntimeScanner.runtimeExists(RuntimeScanner.java:100)
at org.jboss.tools.runtime.ui.RuntimeScanner.access$0(RuntimeScanner.java:98)
at org.jboss.tools.runtime.ui.RuntimeScanner$1.run(RuntimeScanner.java:50)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)

If you try to open the Runtime Detection preference page, you will get a dialog with the message "The currently displayed page contains invalid values" as well as the following exception in the error log:

!ENTRY org.eclipse.jface 4 2 2012-09-08 23:04:09.526
!MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.jface".
!STACK 0
java.lang.NullPointerException
at org.jboss.tools.runtime.ui.preferences.RuntimePreferencePage.createRuntimePathsButtons(RuntimePreferencePage.java:424)
at org.jboss.tools.runtime.ui.preferences.RuntimePreferencePage.createRuntimePathViewer(RuntimePreferencePage.java:256)
at org.jboss.tools.runtime.ui.preferences.RuntimePreferencePage.createContents(RuntimePreferencePage.java:130)
at org.eclipse.jface.preference.PreferencePage.createControl(PreferencePage.java:232)
at org.eclipse.jface.preference.PreferenceDialog.createPageControl(PreferenceDialog.java:1502)
at org.eclipse.jface.preference.PreferenceDialog$14.run(PreferenceDialog.java:1259)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)