git log history simplification problem

Hi,

I was trying to understand the history of a piece of code in LibreOffice
and I'm facing a behaviour of git-log which is not something I can
explain. I'm not sure if this is a git bug or a user error. ;)

Here is the situation:

git clone git://anongit.freedesktop.org/libreoffice/core
cd core
git log --full-history -p -S'mnTitleBarHeight =' sd/source/ui/dlg/PaneDockingWindow.cxx

Here the first output I get from git-log is
b390fae1706b9c511158a03e4fd61f263be4e511, where you can see that the
commit *added* that string. So it should be there on master, I would
assume.

But then I run:

git grep 'mnTitleBarHeight =' sd

and it's not there. Am I missing something, as in e.g. even with
--full-history git-log does some simplification?

Thanks,

Miklos