My xunit configuration is set to report a build as failure if more than 10 tests fail total, or if there is at least 1 new failing test.

This "1 new failing test" only works OK as long as we have no compilation failures and/or aborted builds. If we have a build with no recorded test results, the previous amount of failing tests is always 0. I think it should be compared to the amount of failing tests in the previous build with recorded test results.