Tests run time is completely off in rollups

I use ReSharper 9 test runner to run my tests grouping by Category (which basically groups by Category+Class name).
When I mark the option to "Show Time", I see that the numbers are completely off in the rollups, something like:

EVT               [0:16.000] Success
  MyClassA    [0:07.000] Success
    MyTest1    [0:02.000] Success
    MyTest2    [0:24.000] Success
    MyTest2    [0:06.000] Success


BTW, all of those numbers are made up, but still, I see no correlation between the individual tests and the rollups... sometimes the rollup is bigger and sometimes smaller

I don't remember having this issue with ReSharper 8. The only issue I saw back then is that some of my categories (Functional) sometimes took more than an hour, so the displayed time would truncate hours, so if the tests took 2h20m, I would just see 20:00.000. I don't know if this issue still occurs in R#9 given that the time is completely broken now
I'm using MSTest.