The license header in wintab.h says:
This license does not explicitly allow for modification and for making derived works. This makes it incompatible with DFSG.
qt_attribution.json says that this file is public domain, which is not true.
Moreover, the website says that they are not distributing the software anymore due to a patent lawsuit settlement.
This is not a big problem for us in Debian, as we will just strip that directory from the tarballs, but I am filing this bug to make you aware of these issues.