What does search in a non-existing group do?

Hi, out of curiosity (and because the question arose in another thread):

set theResults to search " kind:markdown" in missing value

returns results from only one database whereas

set theResults to search " kind:markdown"

returns (as expeceted and documented) results from all databases.
I’m wondering

  • why the search in a non-existing group returns anything at all
  • what the rationale for returning values from only one database is

A missing value is like no parameter but due to a bug the results are not identical, the next release will fix this.