[Details] It happened because ARDOUR::Butler::thread_work() was called before Buttler::map_parameters() method was called, which sets up the correct buffering parameters (set_buffering_parameters () call) according to chosen preset.
I've added this calls into Butler::start_thread () to make sure everything is set up and ready for use for Butler.
This is a hot fix, because it requires the review from Paul Davis, and probably more gentle solution. But it's possible this commit may become the main solution itself.
ff8b4693bf