Debugging in Eclipse across different JRE versions

From time to time, we get issues that only occur with a particular version of the JRE. Setting a break point and then stepping into the JRE sources proved to be troublesome as the mapping between which JRE was being used and the JRE source was not correct. Fortunately, I've recently discovered the issue. While the runtime JRE was set to one version, the actual classpath had a different JRE. The key is to remember to also change the classpath to use the same JRE as the runtime JRE. 

I keep forgetting this, so basically, note to self...