You are right.
It is fixed in SVN 614.
If you want to modify yourself, here is how.
Open up img.utils.php and goto line 1196. It should read:
if ( !in_array( fileHandler::getImageType($file), $this->allowedFiles ) ) {
change this to:
if ( !in_array( fileHandler::getImageType($extractDir . $file), $this->allowedFiles ) ) {
It now will provide the correct path to the getImageType() function.
Let me know if this fixes your problem.
Thanks.