Forums / Questions and Answers / Magic protection n merging

If I cast magic protection on an army, then merge another army into it, will that just remove the spell? If not, then does it weaken it? and if so, then by how much?

When merging, all helpful spell affects (invisibility, bless, MP, etc) will go away on the new army no matter which of the two starts with it (merged in army or army merging in)