Turning off parallel builds in Eclipse (max builds set to 1) does not help.
Edit 1 (won’t let me create more posts):
Also another relevant link:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=550144
Edit 2: I just had an idea… will try later… Since these errors always appear on static resource files and (I think I remember that) there is a way to configure Eclipse to not copy them to the output folder (filter them) I could do that and try to add the source folders themselves to the (runtime) classpath.