Hi Moritz, actually the report generation for those cases (called an "assert" instead of a crash) isn't hooked up in v4, I'll re-enable it for the next beta.

There may be some information about it in the log though, you can show the log by running this script:
script: moi.ui.createDialog( 'ShowLog.htm' );

Could you please run that copy any text in there and send it to me here or e-mail to moi@moi3d.com ?

Thanks, - Michael