I am still experiencing this on xUnit 1.78 with Jenkins 1.544 (Windows).
In the "Testresult" overview, testcases are marked with "Age: 1day". When i click that testcase, i see 12 testruns with "regression" and the last one with "failed". So the actual data for the testcase seems to be correct but the parsing for the "testresult" overview is somewhat off.
Please tell me which other information might be useful for you.