Title says it all. If you use an exotic that gives you x4 surges from class ability use, those surges will not apply to a weapon that has the Permeability trait, even if the new weapon energy matches the surge type. For example, if I have a Doomed Petitioner with Permeability, and I use my class ability with Mask of Bakris on, the energy of the weapon will change to Stasis, but it will not be granted the x4 Surges that it should be granted from Mask of Bakris. Same thing happens with Icefall Mantle. Not sure if this is something that is known or an intended restriction on the perk.