Quite often people are relieving in a position or are hired on a temporary basis. In these situations the position is eventually advertised and usually the temporary incumbent applies along with anyone else who is interested.
Many of the relieving incumbents take it for granted that because they are already acting in the role, the job will be given to them and consequently a blasé approach is taken. As a result, more often than not, they don’t get the job. When this happens, they sometimes react angrily and don’t understand that it is their own failure to prepare appropriately that has brought about their lack of success.
If you have been acting in a role and have now applied for permanency in the position, prepare for it as you would if you were coming at it cold, that is, as though you have never worked for the organisation before. This approach will give you the best chance of success.