First, if you have taken more than five days of leave without pay during a school year then your holiday pay will be reduced. The reduction is at a rate of 0.3 days holiday pay for every day of leave without pay. If you took a holiday overseas for two weeks during term time, this is a total of 14 days leave because weekends count in such a situation. You will then lose a further 4.2 days, rounded to 4 days holiday pay. This will usually be deducted in the first vacation period after you return.
The second exception is when you resign and leave teaching, either during or at the end of a school year. In those situations you will be paid, on cessation of duty, any holiday pay owing. This is calculated generally as 0.3 days holiday pay for each day of paid service (including weekends), minus any holiday pay already paid out in earlier vacation periods.