String.Concat fails in nested node

Seems String.concat passes inputs seperately when nested in a node as seen below. So in the case below I get an excel called test with a sheet called just cumulative and a file called book3(I think the number im inputing not sure why the book part is there) instead of a file called Analysis_Data with sheet called Cumulative2. Works as expected when not nested. Am I missing anything or is this a bug?