I just "linked" some files for std.experimental.logger into my project and wondered why the IDE locks up / doesn't auto-complete. Copying the files into the project directory works. Then I noticed that although the IDE sees and can load the files and they get compiled properly, Mono-D doesn't find them unless I also add their origin as a import path to the project.
Reproducible by using "add existing directory" on a project and afterwards selecting "link files" instead of "copy files".