This will probably be because it has been requested as other leave rather than holiday.
Other leave is never deducted from the holiday entitlement.
Should you not wish the other leave reason 'TOIL' to be available to your employees to use, you should edit this reason and re-name it with a dash or a dot. This will deter employees from using it.
You can do this under your Settings>Absence Settings>Other leave reasons>edit TOIL: