***So , I was having this same issue:* **
The Problem:
I assume that you placed a border around your text box and decided to place the hide and toggle element to your text box. or your Rows are not stepped down. Two solutions, I think the first solution is what you are looking for:
Solution 1:
I Noticed that SRSS reporting also has this grouping feature by rows. So to hide the text in the textbox without losing borders is to create a step-down feature within the grouping. So basically you can assign hide text box property without disturbing the rows above the textbox. This may be a better solution.
Solution 2:
You must instead place the border attribute to your text box and place the hide and toggle function on the individual groups. So for you, you have to remove the hide + toggle feature on the textbox. Right click the group element in your "rows" or "columns" and assign your drilldown hide + toggle feature on the group elements. In other words: "group properties" not "text box properties"
I hope this re-solve your issue.