If a test build was canceled like at [1] then there obviously are no stats about the number of failed / passed tests available. Currently, this leads to the next build at [2] to display no relative stats but just "TAP Test Results (69 failures )". I would expect the TAP plugin to take only a previously completed test build into account when calculating the relative stats. I.e. the build at [1] should use the build at [3] to calculate the relative stats and "TAP Test Results (69 failures / -60)" in this particular case.

[1] http://mingwgitdevenv.cloudapp.net/job/mingwGitDevEnv-test/9/
[2] http://mingwgitdevenv.cloudapp.net/job/mingwGitDevEnv-test/10/
[3] http://mingwgitdevenv.cloudapp.net/job/mingwGitDevEnv-test/8/