Occasionally and randomly, collapsible regions may not render correctly. You can work around this by collapsing and expanding all regions.
This is a screenshot of the bug in action: a collapsible region does not expand correctly, and ISE draws some artifacts:
To work around this bug, press
CTRL+M twice. Or, you can use the collapse toolbar and collapse a specific region level:
Currently, the bug occurs randomly. If you identify steps to safely reproduce this behavior, please leave a comment to help us fix the bug.