I was attempting to apply the Vox Extrude tool after making a selection, the layer was in surface mode, but it was the only layer visible. There were several other layers but they were turned off.
I was having some odd behavior with the auto-save previously where I would see the counter counting down and I would ctrl-s save, which would cause the count-down to disappear as it should but then it would re-appear and start counting where it left off before I saved, as though it wasn't recognizing my save attempt.
Then, when I put my above note into the crash reporter and tried to send my crash I got this error:
Fatal error: Cannot access empty property in /var/www/vhosts/3dcoat.com/httpdocs/typo3conf/ext/bug_report/pi1/class.tx_bugreport_pi1.php on line 107
So I've attached my crash output to this post as well as the above comments. Hope that helps fix things!