Well, "shit happens" (c) <!-- s:lol: --><img src="{SMILIES_PATH}/icon_lol.gif" alt=":lol:" title="Laughing" /><!-- s:lol: -->
I think it is more likely just an occasional error, which can always happen, even in most good-build programs.
And I am not sure it is because of radius damage or thing thrust. More possibly, IMHO, it refers to collision checking.