Adding values to a repeatable IPTC tag segfaults

This happens with pyexiv2 0.2 (development branch) compiled against libexiv2 0.19.

Adding a value to a repeatable IPTC tag (or setting the value of a repeatable IPTC tag to an non-empty list that contains more elements than the previous value) raises a segmentation fault. Test script to reproduce:

import pyexiv2
m = pyexiv2.ImageMetadata('image.jpg')
m.read()
key = 'Iptc.Application2.Keywords'

# If the tag is not present in the image:
m[key] = pyexiv2.IptcTag(key, ['one'])

# Or if the tag is present with, say, two values:
m[key].values = ['one', 'two', 'three']

# This also segfaults:
m[key].values.append('more')

Note that setting the value to the empty list behaves as expected (and doesn't raise a segmentation fault): after writing back the metadata, the tag is not present in the image any longer. Setting the value to the empty list when the tag was not previously present also works.