In 6.3.1 command “executeScript return window.history.back(-1);” (as well as back()) results not in “make one step - go back to previous page”, but in deeper return through the history. Execution “hangs” on the executeScript till browser goes the way back. I didn’t check, but it looks like it goes 2 times back, maybe.
6.2.8 works just fine (execution is fast and it makes only one step back in the history).