try this:

function test_event()

{
swit(event_type == EVENT_BLOCK) sys_exit("bye bye ...");
}
switch (event_type)
{
case EVENT_BLOCK:
sys_exit("bye bye ...");
return; //try with return and without(just remove this line
}

The smaller the bug, the harder it is to kill.
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Forklift DEMO (3dgs)