I have the "Avenue Theme for Wordpress" and it has the Nivo Slider built-in. My blog is "http://dailyfix.gr" and when the page is left for some time, then the slider titles transform to "semi-transparent" or just vanish...!
Here are the screenshots I took.
Titles with no problem :
Semi-Transparent Titles :
Vanished Titles :
This issue is visible in Firefox, Chrome, IE, Opera. Test it by entering to http://dailyfix.gr and let it sit there for a minute or two. Then the problem will come.
PS : Sorry for my English...