See for example the attached expected result that I grabbed from http://build.webkit.org/results/EFL%20Linux%2064-bit%20Debug%20WK2/r135957%20%286418%29.zip . Garbage can be observed at the right side.
Created attachment 176734 [details]
example of the issue
I spent all day running tests today, but cannot get the same type of artifacts that we get on the buildbot, in my local environment.
That makes it very difficult to debug.
It was not the scrollbar that made the tests flaky, but resizing the window in one test affected the gl viewport size in all tests on that worker.
*** This bug has been marked as a duplicate of bug 104139 ***