From Eclipse (XP), passed at 1st attempt, failed at the 2nd!
I am not familiar with this part of the code so it would be too much work to track it all the way myself, but I think I can now provide sufficient information for solving it.
In Eclipse, after cleaning the project the test passes, and then start failing in all successive runs.
So I assume when you run it isolated you also do clean, which covers Eclipse's clean (and more).
I tracked the content of the cleaned relevant dir before and after the test - it is (trunk/)bin/solr - there's only one file that differs between the runs - this is bin/solr/shared/solr.xml.
Not sure if this is a bug in the test not cleaning after itself or a bug in the code that reads the configuration...
I'll attach here the two file so that you can compare them.