Yes, in a nutshell. Windfalls (basically unearned income) are treated differently from extra (earned) income.
But do make sure you get the 10% disregard on that extra earned income --- some proposals (such as mine) are drafted as a straight 50/50 split, with no 10% disregard.
It is a steep learning curve, but sit down with proposal in one hand and a cuppa in the other and read it all through. Unfortunately, these days, things (certainly with a few particular providers) are not as 'standard' as they were intended to be and sometimes there is confusion, but never be afraid to ask.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk