Yes, this is pretty much standard. PPI is an asset of the IVA and the arrangement will not complete until it is dealt with. You can either assign it now or wait until your IP is happy it has been finished with ...which could take quite some time.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014
I agree with Foggy that it won't hurt to sign it and it means your IVA will finish sooner rather than later.
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk