Faraó

This shouldn't happen, but unfortunately there are many clients (proofreaders/revisors working for them) who do that.
I think that correcting translator's style isn't an ethic procedure. When I've a proofreading I'm always alerted by my client or agency to not interfere with stylistics (unless I see a critical point which needs to be changed), and I keep and comply with those instructions.
I've discussed this issue with some colleagues too, and I was told that they do that for some reasons: show to the client that they worked closely on the revision, and sometimes in worse situations they do that to "steal" us the job/client.
You're saying it was your client who corrected your translation "flow"; it's something that happened to me too once, but in the end I've found out that it wasn't my client, but someone else... someone I believe didn't have even a qualification in translation!
I'm not saying that this could happen to you, but we should always ask for any explanation from our clients in this situation, and then give them our feedback on the matter.

__________________
نحن من مصر