We are really sorry for the inconvenience!
The issue you reported us seems rather strange, we have never received such a feedback. Anyway, could you once more time try to disable this feature (JustCode | Options | Visual Features | Structural Highlighting | disable the checkbox for 'Structural Highlighting')
and check if the lines are gone (have in mind that you might need to scroll up/down the view for the document for the changes to take effect). If they are still appearing, could you send us your settings file (%appdata%\JustCode\settings-justcode.xml)
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items