QImageReader::text() fails if key contains colon

I am using Qt 4.7.4 on Linux and I am trying to use QImageReader to read PNG meta data from thumbnail images. The keys of the meta data contain colons as required by the standard from freedesktop.org. QImageReader fails to parse these keys correctly.

For example, such a file contains the keys "Thumb::URI", "Thumb::MTime", and "Software". But QImageReader::textKeys() returns [ "Thumb", "Software" ] and it is impossible to get the values for the keys "Thumb::URI" and "Thumb::MTime".