I’m having the same issue, and I tried the custom CSS, but it doesn’t work. I’ve tried putting it in the theme’s custom CSS, and in the custom styles for the particular Master Slide I’m working on, but neither place corrected the issue. I also tried using .ms-slide-info, as that’s what shows up in firebug.
So, to verify, here’s what I’ve tried in both the theme’s custom CSS and in the custom styles for the particular slide I’m trying to fix:
.ms-info { min-height: 1px;}
.ms-slide-info { min-height: 1px;}
Any other ideas?