İso trim unsliptting surface

Hi Everyone,

I have a loft surface that I split with a curve and I want to only work on one part of the split. So I deleted the part I dont need.

I am trying to divide the remaing surface using divide and isotrim. When i plug the isotrim component it ignores the split operation and recreates the untrimmed surface. How can i avoid this. Any help would be much appreciated. Thanks.