Yep, though I looked through the decode code for cleanup like things that weren't getting called. 

Libtiff's error state is here: https://github.com/python-imaging/Pillow/blob/master/libImaging/TiffDecode.c#L222 , and farther down at line 237 as well. 

WebP's one free is here: https://github.com/wiredfool/Pillow/blob/11a0fb5f76abf94dc91cf5f2cb8eb1bf2c60828a/_webp.c#L95 . And looking at that, there's another call needed right above Py_RETURN_NONE at line 75.