I am guessing that you are talking about the rollback bar. This does what it says - keeps features under it from processing and taking regen time.
It could also be the feature freeze bar (if enabled)
Lucian, would you please post a picture showing the black bar?
Sorry, I was on holiday last week and my problem was solved by restarting my computer.If appears again, I will take pictures for show you.Thank you too all.