Text Shift Uncontrollably Inside Accordion Widget

Question

Guys hi! I've been crashing my head for two days with this. Hope you will provide some help!
I have an Accordion Widget with a very long text block inside one of the boxes (a list with over 80 lines). On the background to each second line I put a grey rectange shape just to give some contrast to the lines in the list. In the project all the rectangles are prefectly aligned to be right behind the lines. But when I publish the site I definately see that the rectangles shift up or down.
Is it a bug and the widget simply cannon handle correctly so many elements insie the feiled or am i missing something here?
Many thanks in advance for your advice!! You might be saving me from insanity here;)
UPDATE!! It was not the shapes but the text that was shifting. I fave some items on the list that consists of two lines. That's where I changed the leading betwin those two lines from 200% (for separate items in the list) to 146% between two lines (for the items that cosist of two lines of the text). That somehow couses the text to shift in the preview mode xompared to the design mode. When I make the leading unilateral throghout the entire textbox everything stands in place.
Still the problem remains unsolved.

Answer 1

Zak. thank you very much!
And sorry for coming back so late on this.
You solution perfectly solved the problem.
On the downside,) I did have to change the layout and reformat the site to submit it to the client because the deadline came before I got your reply.
Perhaps the "Round Leading to a Whole Number" setting should be checked by default to avoid this kind of problems for other users in the future.
Anyway, a million thanks!