> Initially, Paint.net was released under a modified version of the MIT License, with the exclusion of the installer, text, and graphics. It was completely open-source, but because breaches of license, all resource files (such as interface text and icons) were released under a non-free Creative Commons license forbidding modification, and the installer was made closed-source. Version 3.36 was initially released as partial open-source, but Brewster later took down the source code, citing problems with plagiarism. In version 3.5, paint.net became proprietary software. Users are now prohibited from modifying it.[1]

[1]: https://en.wikipedia.org/wiki/Paint.net#History

Paint.NET was open source, but a pirate would download the code, put their name over the author’s, and click build. That’s a very clear case of copyright violation, but the author decided it wasn’t worth the effort (especially if the pirate is in another country).

https://blog.getpaint.net/2007/12/04/freeware-authors-beware...

The author blogged about it in 2009 [1]

TL;DR They used a MIT licence and other people were selling broken, rebranded cashgrab copies without changing things like the installer or crash logs being sent to the author etc

[1] https://blog.getpaint.net/2009/11/06/a-new-license-for-paint...

So why isn't this a problem for other open source software? Or is it? Is it only because of the high demand for a cheaper/free Photoshop alternative?

It is.

It's more than frustrating to have crash logs that don't refer to your code and contain access tokens or similar data because the author of the 'rebranded' software doesn't care about user privacy.