I'm creating this post because this was an issue for a long time, since last summer and I never figured out how to fix it, until tonight. I had to go into the item file and make a few changes and poof now it works. Note, that you have to have fists queued up as your current weapon and if you do, then you will automatically switch to the Serpentis Claws after shapeshifting. If you don't have your fists queued up as your weapon, then the weapon queued up will simply disappear and you will have to manually change over to the Serpentis Claws to use it. That's how the vanilla game was with Protean claws and that's how Serpentis works too now.