grep -v exit code on empty files

[David Jones]

The man page for grep claims:

> Normally, exit status is 0 if matches were found, and 1 if  no  matches
> were  found.   (The  -v  option  inverts the sense of the exit status.)

So since
: | grep e

exits with 1 (no matches found)
I would expect
: | grep -v e
to exit with 0 (-v inverts the sense).
But it doesn't.
: | grep -v e
exits with 1

Bug in grep or in the documentation?  You decide.  I can't decide.  And 
I can't be bothered to trawl through the spec for an authoratative 
answer either.

Cheers,
 drj