Outside the debugger, it is not normally possible to trigger a second FKISS event while one is already running (the only exception to this is when two or more alarms are triggered within the same wimp poll).
However, it is obvious that (unless action is taken to avoid it), when the debugger is halted this rule would be very easy to break (for example, moving a cel may trigger a drop event, changing sets can trigger a set event, and so on). This could have very bizarre repercussions on the way that scripts behave (they are not, in general, re-entrant).
The debugger avoids these problems by using the following techniques: