Why won't the multi-excerpt include macro find the page where they are included

We created a space (let´s call ist SpaceA) where we collect different to do´s for different project states. We want to copy SpaceA to other projectspaces (in this example SpaceP) for checklisiting this items. 

We used the macros Multiexcerpt for defining the source and Multiexcerpt include for collecting the sources in a list in Space A. That worked without problems.

But after copied this list/Site (containing the multiexcerpt includes) from SpaceA to SpaceP we get an error and the list doesnt show the content from the source (in SpaceA).

Error message: the site containing the multiexcerpt doesnt exist. please check the macro.

We cannot fix it (neither via cache eg).

How do we can copy variable content from one source to another with this macros without getting an error?