Hi Animajor -
I am running some tests here, but it looks to be a specific setup issue you have in your Sequencer that has caused the crash. I am fairly certain I can reproduce this if I replicate the circumstances you have setup in your project. Is there any way you can share the level sequencer file in a very simple sample project that also crashes for you? If you would like to keep it private, feel free to link the project to me via the Engine Forums.
Thank You and I will continue to try to replicate in the meantime-
Eric Ketchum