I had same problems with 18.2 and 18.3 with my X8-HP: system become freezed always I tried to stop a film.as Yorker and Kodlz have reported.
It is true that the problem is solved if HW acceleration is disconnected but it is not a good solution...
I found another solution (just following the datrh's instructions he gives in the first page!!) you have to set "adjust display refresh rate" to "Always". Then everything goes OK (at least with 18.3).