Actually, the LICENSE file is for their project (which amusingly, he seems to have gone from the original GPLv2 to MIT a year earlier: https://github.com/wordpress-mobile/WordPress-Editor-iOS/com...).

Even at that time, the source code included from the other project seems to have the embedded MIT license notice (e.g. https://github.com/wordpress-mobile/WordPress-Editor-iOS/blo...).

And in the README.md they have attribution, mentioning the licenses of the underlying dependencies.

tl;dr: The LICENSE file is for this project, not the underlying libraries they copy-pasted in (which other than say the png files, seem to have their MIT/BSD info in them).

That's a good reason to include license terms in each file. I don't think that Wordpress people were malicious here. The LICENSE file usually contains the global licensing terms (as seen in many GNU projects). Each source file should still contain the license or a mention of the license. MIT-like licenses are usually put verbatim in each files, while verbose licenses like GPL just get a pointer to the LICENSE file.

On some files, the MIT license is correctly present at the top of the file:

https://github.com/wordpress-mobile/WordPress-Editor-iOS/blo...

Good find.

Any source file found before Mar 20, 2015 should be covered by Neil Stoker's copyright and the MIT license. This includes WordPress derived code.

MIT license doesn't cover derived code. Only attribution is needed.

But that doesn't mean you can strip out the license either.

Well, you can relicense the MIT-licensed code. They might have had to include the text of the MIT-licensed component license, but that would still have no effect on the license of the derivative work - it would be GPL.

That license change would only apply to the changes and additions, any of the original code would still be MIT licensed, also if the changes are trivial then the whole re-license might fall through.

Copyright would still lie with the original authors as well, after all sub-licensing allows you to pass on the rights that you already have, but does not give you any new rights.

Since the MIT license is mostly a super-set of the GPL you will lose some of the MIT parts if you sublicense but if you wish to gain more rights than what the MIT license already provides you with it will likely not work when tested in court. The best way to deal with stuff like this is to stick to the original license unless you have consulted with an IP lawyer that signed off on your plan, it is very easy to get these things subtly wrong.

There were over 1000+ commits made in over a year -- all of those changes and improvements are GPL. (You can make GPL mods to MIT code and release those all as GPL.) If Wix had used the original ZSSRichTextEditor they would have been fine, but they didn't.

The key thing to understand is that being “compatible” with the GPL means that you can take code written under an MIT license , and put a GPL license on it if you want to. The MIT license allows for this, but, the reverse is not true. The GPL does not allow you to take GPL code and change the license to MIT, and it definitely doesn't allow you to take open GPL code, and make it proprietary.