[gentoo-user] Is it a bug if revdep-rebuild catches something that preserved-rebuild doesn't?

[Nikos Chantziaras]

When running:

  emerge @preserved-rebuild
and nothing is found that needs a rebuild, but:

  revdep-rebuild -i

does find something, should it be considered a bug with the 
preserved-rebuild mechanism and be reported, or is this expected to 
happen from to time?