Opacity on a title does not work when applying a transition to another title

I often build titles from white pages with writings,  that clients give me. I put a colorful background then I export the page into a jpg, apply a multiply opacity to the page. The white color goes away and the writing is all that's left. All is fine unless I want to put a transition with another title constructed in a similar way.  Then the white from the paper show up again during the transition. I thought that nesting the title would  solve the problem. But actually not. Am I doing something wrong or is there a trick I am not aware of?

Thank You!