I think there's a default widget that makes caretakers patrol automatically, maybe you've accidentally disabled it. The 'line', aka nanospray, is not visible with some graphic cards or some settings i think, hope someone can explain you more.
pro tip: post your system specifications if you have (graphical) bugs like this. It will help to answer your question
also: maybe post in 'help and bugs' forum section instead of in 'general discussion'
