This bug tracks changes to webkitgtkdriver that should be made in light of https://bugs.webkit.org/show_bug.cgi?id=191155. Basically, any two states may only have one difference between them. Otherwise, the ordering of events that happen in the state transition is not specified. See the attachment for what safaridriver sends when running this test case.
Created attachment 356650 [details]
Protocol trace from safaridriver (doesn't crash)