can't save tiff exif

[viponedream]

it handle jpg, png well,
but when i open a tiff file and change the same exif, it went wrong

File "C:\Python\Lib\site-packages\PIL\TiffImagePlugin.py", line 1647, in _save
e = Image._getencoder(im.mode, "libtiff", a, im.encoderconfig)
File "C:\Python\Lib\site-packages\PIL\Image.py", line 477, in _getencoder
return encoder(mode, *args + extra)
SystemError: returned a result with an error set