I know it's old, but I think I figured out what was causing this bug. The array of file names in the temporary files is getting sent to "getImageType" in the batchupload_2 function in images.html.php
it fails gracefully, but warnings are still annoying...
Can add
if ( is_array($filename))
{
continue;
}
directly after the foreach loop around line 575 in images.html.php
It's sloppy, yeah, but works. Keeps error_log from getting too cluttered. I'll put it on svn for legacy mode, might work on v2 too ?