Border settings not saving in SSRS

This may sound silly to some but I've written a note because I spent time googling and still didn't find an answer.

My situation is that I wanted to put an expression to format the border (empty cells have a border and non-empty don't). This was so that a grid would show for empty spaces.

I wasn't getting very far because I'd even ask the border to be grey and save the project but when I come back to the setting, it's still black.

I found that you have to select a color or expression first, then define which border (top, right, bottom, left) the settings apply to...

Mad. 1. Type your expressions/specify color first:

2. Specify which border of the cell this applies to: