iepngfix.htc has the following licene:
// Free usage permitted as long as this notice remains intact.
This is not a free license (for one thing, it doesn't permit modifications) and certainly not GPL-compatible. You might want to upgrade your copy of IE PNG Fix, as the current version is available under the LGPL 2.1 (or later) license.
I do not agree with the conclusion that this is not a free license: even if modification of the file is not explicitely mentioned,
the "as long as this notice remains intact" does not make any sense unless modification is permittet, hence I would imply it is.
That said, updating IE PNG Fix should/could be done.
I propose to either just close this bug or remove the iepngfix (workaround for IE < 7) from Docutils.
Please remove it. It's 2020, and there is absolutely no need to support IE < 7.
IE PNG Fix is removed in r8729.
Fixed in Docutils 0.18.