Yes, the arm should pop of with a bit of pressure. The two materials tend to freeze together a bit so any type of gentle prying you can accomplish would be an asset. However, there has been much debate over the best remedy for this particular problem. Read further below.
Check this old thread out. It includes a link to another thread which further discussed the problem and potential fixes. It also akins the 'fault' to Marylin Monroe's mole.
Good luck with it,