Dear Sir, Madam,
I just pushed some commits to a private bitbucket repo (dcnieho/matlab-optglass). For commit 4dca351f5da5, for every file changed in the commit the changeset notes "File contents unchanged." I did have a little trouble as i amended this commit and then later accidentaly tried to merge the remote (unamended) commit back in. Cleaned that up though, and did a push --mirror. Smartgit shows the file diffs normally and cloning the repo from bitbucket to local destination also gets me everything in the right state.
So i'm not sure if this is just my fault or if there is a little bug in the bitbucket interface, as other interfaces do show the diffs.