Failed to close properly.

Failed to close properly.

1. Menu -> Mockup -> Quit Balsamiq Mockup does not work, the window stays;

2. Click on the close button of the window does close the window but 'ps -ef | grep mockups' shows it's still there;

3. subsequent launching failed (probably because the previous instance is still 'running'?)

Only notice this problem after upgrade to 1.5.13.
Env: linux, xfce 4.4.2;