1. Go to advanced output
2. Add 2 masks
3. Start edit points on them
4. After 2-3 edits all masks stop to be editable. You can drag points around, but they are not changing the output anymore.
Here is a video of a process http://take.ms/qfQMI
MacBook Pro (Retina, 15-inch, Late 2013)
Graphics Intel Iris Pro 1536 MB
Arena 5.0.2
