I was planning to do a PR, but  I couldn't get the game to build on my device. Do you want to help me, @Atrik?

Certainly, thank you.

It reminds me to do something with: https://github.com/AlexanderOlkhovskiy/0ad-space 

Perhaps theyre suggesting this hypothesis? https://en.wikipedia.org/wiki/Nordwestblock

@razieve thanks for reporting this. I can confirm this is a ModernGUI bug on the development version.  A condition was poorly written which created this ghost foundation in some edge cases. It will be fixed next time I push my local work. In the meantime you don't have to worry about it affecting your game. This foundation placement doesn't consume any resources, nor creat any obstruction of any kind. Basically it doesn't affect anything, but you can still delete it to make it disappear. If you want, you can also enable 'global queue' feature to make this work, where builders will start building the foundation once the required resources are reached.