'git replace' and pushing

[Cory Fields <FOSS@AtlasTechnologiesInc.com>]

I am having some trouble understanding how a replaced object (commit)
should behave when pushed to a remote repo. Here's my scenario:

We are moving from svn to git. Our svn repo is huge, and most of the
history is useless. To save space, I would like to do a 50/50 split so
that when the repo is cloned, 50% is seen by default, and the
historical 50% can be seen by fetching the replacement history. I've
done this by creating a phony snapshot at 3 then using a 'replace' to
put the others on top. The history is purely linear.

1---2---3---4---5
                 \---4---5

When the replacement is in place, the repo is half size (commit-wise)
as expected. The problem is that 'git push' does not honor the
replace. So when I push, all objects go with it, which defeats the
purpose. The only way that seams to work is doing a filter-branch and
replacing the other way.

Is this by design? I would really like a way to split the repo without
breaking hashes for the developers that have already begun using git
svn.

Thanks,
Cory