grep --ignore-case fails with --only-matching

[BISHOP Michaël]

When searching for a case-insensitive pattern, grep is able to
correctly identify the matching line when using --ignore-case. 
However, when --only-matching is added, grep passes nothing and returns
zero.

I didn't notice anything in the man pages stating that these two
options are incompatible; did I miss something or did grep?
> address@hidden mbishop $ echo "This is An _expression_." |
> grep --ignore-case _expression_
> This is An _expression_.
> address@hidden mbishop $ echo "This is An _expression_." | grep
> --ignore-case --only-matching _expression_
> address@hidden mbishop $ echo $?
> 0
-- 
Michaël A. Bishop
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Clemson, SC  29631
Etats-Unis / USA
(864) 506-6040

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