Managed Solution Not Overwriting Form Changes When Imported

I have abcd entity with 4 forms. In a form that I'm facing the problem while importing the solution.the changes not reflected in target entity.

In a form already I've one section lets called  section A.In that section I added new Iframe and deploy the solution in SIT.

Now I delete the section from form for some reasons in dev.

After I'm creating the same section with same name but different Iframe (Which means url is different) and exported the solution as a managed one and import it in SIT. In dev I'm having only one section.

But In SIT I have two sections (Still old section exists and new one also) with the same name.I deleted the old one and recreated the section with same name . But two sections got displayed in SIT but not in dev.