P.P.S.: I hang my head in shame.
I remembered that we've been using mods, namely CBM, and I rechecked, the mod that I was using for the replay differed from the one that I used on the server, although they've both been named CBM 1.41:
server md5sum: e0393301aa565bc98ad5eff476778a37
client md5sum: 79d3146137c36d8b5ddc4016941690a1
I suppose that Zeldor has been using the same outdated mod like I did. When I watch the battle with the right mod, then I can see correctly that the battle is a little different, with the water elementals gaining more ground early on and a maggot infestation on the Ettin Mandragora which makes it use its Elixir of Life and still kills it in the end, with a huge poison bar before routing. This might have been a wrong alarm, I'm sorry.
Still, if there are battle replays that are wrong, then I recommend checking the server logs that have been generated during hosting (every server admin should make sure to generate full logs and keep them!) with those that are being generated when viewing the replay, like I did here. That's the best way to find out what's wrong. Are there any other known battle replay inconsistencies?