http://sourceforge.net/p/libpng/code/ci/713a20c57d344b558e48ad8be157c2dd751c8815/tree/pngpread.c?diff=4526f546baea7f73097529cb66feb4dbc8da2752
--- pngpread.c
+++ pngpread.c
@@ -234,6 +234,7 @@
          png_error(png_ptr, "Missing PLTE before IDAT");
 
       png_ptr->mode |= PNG_HAVE_IDAT;
+      png_ptr->process_mode = PNG_READ_IDAT_MODE;
 
       if (!(png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))
          if (png_ptr->push_length == 0)