[racket] compile-omit-paths and scribblings field

It appears that compile-omit-paths doesn't prevent a scribble file
from being compiled, which is problematic if the scribble file
requires another module that includes image snips.  We're seeing that
when we PLaneT install a package, that during compilation, we see this
error message:

    raco setup:   write: cannot marshal value that is embedded in
compiled code: (object:image% ...)

However, if we remove the 'scribblings' field from the info.rkt,
things compile cleanly, so we do think there's a bad interaction
between compile-omit-paths and scribblings.  Is this a bug?