I haven't seen any audio delays or problems.
The program is just frozen, does not respond to UI elements, it doesn't redraw the window, and doesn't respond to closing it with the window manager X icon, until the window manager (xfce4) offers to kill it. Then I have to kill jt9 otherwise it complains about that being frozen when restarted. That might be a clue, but I've never used jt9.
I'll install the newest version from unstable and see if it persists.