Thanks for this (old) bug report <http://bugs.gnu.org/18974>.
I cannot reproduce the problem with grep 2.25 on Solaris 10 sparc with cc from Studio 12.5. Perhaps the mbrtowc bug has been fixed. Or perhaps I have not reproduced the scenario (looking at the test, it seems that it depends on a Japanese locale, not a European one). Or perhaps the bug is x86-64 specific. In any event, since grep itself does not depend on the mbrtowc functionality in question, this is not a bug in grep, so I'm closing the grep bug. If someone wants to fix it I suppose they can debug the issue and send a patch to bug-gnulib, but this is low priority.
